Editing Warhammer 40,000/9th Edition Tactics/Space Marines (section)

===Troops===
With the new FOCs, it is possible to make a Battle-Forged list without any Troops at all... but you do need them for CP. Troops are usually where one turns for numbers, as in 9E the player with the most models within 3" of an objective can claim it. You have a lot of options for Troops but they're actually decent this edition. Your basic defensive statline is MEQ with T4, W2, Sv3+, making them quite durable against most enemy small-arms; However, there are no shortage of weapons with S5+ and D2, like autocannons, plasma, and 9th edition has made the ever-common heavy bolter D2.

*'''[[Tactical Squad]]: CORE, 18pts per model.'''  No longer your default choice for Troops tax, Tacs are still viable, but require more forethought compared with Intercessors. Heavy weapons are easier to use now as they get fewer penalties for moving and unlimited split fire exists. This edition encourages you to '''''take them as MSU'''''; less morale vulnerability and multiple units can fit in the same transport. Two five-man units fit inside a Rhino, giving two Serges with Combi-weapons plus two special/heavy weapon guys as opposed to the three a regular ten-man squad have. 
** When deciding between Tacticals and Intercessors, you must consider their intended role, as barebones they're your worst Troops choice. The main advantage over Intercessors are the ability to take special/heavy weapons, so ''use them''. They're basically the same price as Intercessors now, so if you just want cheap Troops, ALWAYS take Intercessors; Tacticals are so much worse in shooting and melee that downgrading isn't remotely worth saving a measly 10pts.
**Per the Jan 2023 rules update, these guys got better. Why? Their wargear is now all free! Mix and match as you wish with your Tac Squads. 10th Edition is likely their last hurrah, so enjoy it with dusting off your old models from 6th and 7th with Grav and Plasma, Meltas and Multi-Meltas, Missile Launcher Tacs, Heavy Flamers, and Lascannons. Who doesn't want an 18 point Lascannon? This also applies to the squad sarge, including combi weapons. 
***
** Tacs can ride in Rhinos, Razorbacks, Drop Pods, and Termites, for Dedicated Transports; Land Raiders, for Heavies; and Stormravens, Stormfangs, Stormwolves, Storm Eagles, and Corvus Blackstars, for Flyers. Firstborn transports tend to be more affordable than their Primaris equivalents (when they exist - there are only Primaris equivalents of the Razorback and Land Raider), which look much more like tanks and mount more guns without really being that much more durable. This means they're far more likely to draw heavy fire, and while this can be an advantage depending on your game plan, it does make Tacs notably better if all you want a cheap, speedy box. Combined with the point above: bring tactical marines if you want to tactically drive tactical heavy weapons in tactical transports to shoot (tactically) your enemies in the face with a tactical melta. For around 1.5 intercessor squads.
** Tacticals generally lose out on stratagems, as many only work with Primaris, and while dropping defensive strats on Troops is usually a waste of points, the lack of Transhuman Physiology might make the difference between holding and losing an objective. One area where Tacticals do have the advantage is mortal wound stratagems; Melta Bomb and Flakk Missile are functionally Tactical only, while Hellfire Shells are Tac or Heavy Intercessor only, and can kick out a surprising amount of damage.
** As a rule of thumb, point rebalances make heavy weapons better choices than special weapons, as even when at a penalty from moving they kick out more damage. The only exception is Assault-type weapons which can shoot after advancing, but since this means your bolters can't fire, it often isn't worth it anyway.
<tabs>
<tab name="Combi-Weapons">
Whenever a combi-weapon has the same cost as a special weapon, it's strictly better; except for a combi-flamer, when the combi-weapon costs more, it's almost always strictly worse.

*'''Combi-Flamer:'''  3.38x the S4 dakka of a bolter hitting your target at 12" (1.69x the dakka of a storm bolter) for less than twice the cost of the base model, but no ability to hit things farther away.  No benefit over a flamer if you advance, but if you don't, 1.29x as good as a flamer; ''current'' point costs have a combiflamer dude costing 1.22x a flamer dude.  For Overwatch, the output is only 1.1x as good as a flamer, meaning combiflamers are ''less'' efficient at Overwatch than flamers.  If you're taking a flamer anyway, or in general have a good plan for ensuring your plan is to engage the enemy at 12" or less, this is a good choice.
**If you have +1 to hit ''and'' your 6s to hit explode into 2 hits ''and'' you can re-roll 1s to hit (but you don't have +2 to hit and you can't re-roll all misses), a storm bolter will outperform a combi-flamer (the combi-flamer will only have 1.17 the dakka while costing 1.2x), but that's difficult to arrange - one way to do it is park Crimson Fists next to a Captain and shoot a large unit.
*'''Combi-Grav:'''  Just no - sure, it costs the same as a grav-gun, but that doesn't fix the crippling range problem the grav half has.  If and only if you took the Long-Range Marksmen successor tactic, the grav half can double at 10.5", which means this can be like an overcharged combi-plasma where you downgrade from S8 to S5 in exchange for firing safely.  If you ''also'' made the poor choice to issue the Sergeant an expensive melee weapon, this can be a good move, because the combi-grav is generally better than non-overcharged plasma, and you may not want to risk your expensive melee weapon.  But why would you do that?
*'''Combi-Melta:''' This can be justified if your other guy has a multi-melta or grav-cannon and you want to help murder something heavy.  Once you're within 12" anyway to make your multi-melta better, the combi-melta is good against the same targets you want the multi-melta for.
*'''Combi-Plasma:''' You can fire this on dual mode without making the plasma less safe now, but it's still a lot of points for what you get, even though it's literally a plasma gun but better.  You probably don't want this. Per 2023 rules update, it's free. Take it.
*'''Storm Bolter:''' Now you're cooking with charcoal: literally twice as good as a bolter at everything.  Not as points efficient as a combi-flamer within 12", but makes your sergeant shoot as hard as two marines, while only costing a fourth more than one.  This should be your default choice if you want to make your tacs more expensive, since the primary job of tacticals is sitting on an objective taking potshots.
</tab>
<tab name="Special Weapons">
*'''Flamer:''' 12" of cheap horde-killing and decent for deterring charges. Unless the rest of your squad is dead, you'll usually get better results sitting in cover with another gun and firing your bolters than advancing and firing this, even if you double up with a combi. Since there's no heavy version for most <Chapters>, this is often all you get if you want flamers.  Generally worthless outside of advancing or Overwatch, because the targets against which this will outperform a Grav-Cannon are very uncommon, but is legitimately useful paired with a combi-flamer in the same squad against GEQ.
*'''Grav-Gun:''' 18" of MEQ-killing. Same price as the heavy version, but half the shots at best and lacks the range of bolters, so if you're abusing your rapid fire range advantage you might not even be able to fire it anyway. Plus, as Rapid Fire and not Assault you can't even justify it by Advancing to turn a corner and get line of sight on a target.  Never, ever take this.
*'''Meltagun:''' 12" sucker-punch for Vehicles and Monsters. The only reason to take this is if you're doubling up with a combi-melta on the Sergeant, and even then you'll only get better results if you have to move to get line-of-sight on a target.  Just take a multi-melta instead - never take this.
** Within a five-man squad, let's compare the advancing combi-melta + meltagun vs moving multi-melta. Both combinations fire two shots, and suffer -1 to their hit rolls for advancing and firing an assault weapon and moving and firing a heavy weapon respectively. The advancing assault meltas gives you a 19-24" threat range (6" move + d6" advance + 12" range) with a 13-18" potential +2D range, while the moving heavy melta gives a 30" threat range (6" move + 24" range) and the same 18" melta range.
*'''Plasma Gun:''' 24" of MEQ-killing. Just 5pts cheaper than the heavy version, but loses blast so it's a worse horde-killer and on average will only break even (for output, meaning it's more points-efficient) against single targets at half range. Changes to Gets Hot mean it's usually a waste of points: safe plasma is outclassed by grav weaponry, and overcharging is a bad idea because without re-rolls you'll blow yourself up in short order and tactical squads just don't put out enough damage to justify a re-roll babysitter. That said, there ''are'' some targets where the plasma gun's one shot, even on safe mode, is more efficient than a bolter's two shots... the problem is that it can't compete with your Heavy choices.  Skip this.
</tab>
<tab name="Heavy Weapons">
*'''Grav-Cannon:''' 30" of premiere MEQ-killing, now just 10pts! It's better than the heavy bolter or a safe plasma cannon at mulching MEQs due to its stats, and far safer than an overcharged plasma cannon without a re-roll babysitter. If you want to kill heavy infantry, this should be your go-to choice.
*'''Heavy Bolter:''' A 36" sidegrade to the grav-cannon. Lower AP and flat D2 instead of only versus models with a 3+ save make it better for dealing with poor-save multi-wound models like Daemons or Monsters, but one fewer shot makes it weaker versus MEQs and the extra 6" range often makes no difference as it's beyond your bolter range anyway. The Hellfire Shell strat can chuck out D3 MWs if you hit, and Imperial Fists shooting a Heavy Bolter gives you additional hits on 6s.
*'''Lascannon:''' 48" of premiere tank-hunting power, now just 15pts! Forces opponents to spread fire across multiple units to get rid of your tank-busting and gives you a backup if your heavy support gets ganked early on. A great choice if your chapter tactics give you one re-roll to hit (or wound) per time the unit shoots, although still not as good as a multi-melta within 24".
*'''Missile launcher:''' 48" of versatility. Worse than lascannons against Monsters and Vehicles, worse than heavy bolters and grav-cannons against ''everything'' (but with more range), but a reliable choice against both. A versatile weapons which gives you options as your unit count dwindles, and so always worth your consideration.
**The Flakk Missile stratagem gives you a surprisingly potent AA punch, if you need it.
*'''Multi-Melta:''' 24" of devastation. Lacks the range of the lascannon but makes up for it in sheer damage. The 9th edition heavy 2 upgrade and Dd6+2 melta re-write means this is absolutely worth it on your mid-field units in comparison to the lascannon, but necessitates a transport and ''will'' attract massive amounts of fire (making for a great potential DISTRACTION unit!). A great choice for Salamanders (or the successor tactic for re-rolling 1 hit per time the unit shoots), whose free re-roll is more efficient on single high-power rolls than those that rely on volume of fire.
*'''Plasma cannon:''' 36" of completely wasted points. Multi-meltas and lascannons will do better against vehicles and grav-cannons will more reliably chew through MEQs if you don't overcharge. Overcharged it's still worse versus Vehicles and without a babysitter you've got an almost 50/50 chance of blowing yourself up if you fire all three shots. Even with babysitters, it's still around an 8% chance and honestly? A babysitter isn't well-spent on a single heavy weapon when they could be buffing four times that in a unit of Devastators or whatever. Avoid. With the 2023 rules updates, it could be great with Dark Angels and Weapons of the Dark Age - it's free! 
</tab>
<tab name="Melee/Pistol Weapons">
Your Sergeant can swap out his pistol for one of these.

*'''Astartes Chainsword:''' Auto-include, because it's free and in any context where you'd want to shoot your bolt pistol, you can swing the chainsword ''first''.  Without a very, very good reason, this should be what your Sergeant carries.
*'''Bolt Pistol:''' In any of the rare circumstances where you'd want to shoot this, you're better off with a chainsword.  Hard pass.
*'''Grav Pistol:''' If you insist on taking a pistol and you aren't Deathwatch or Blood Angels, this is the best one: a full 12" range means it outperforms half a grav-gun for half the cost of one.  But it's less efficient than a combi-melta, so why bother?
*'''Hand Flamer:''' If you're Deathwatch or Blood Angels, this is deceptively useful: terrible for the things you want a pistol for compared to just taking a Lighting Claw, but you can take it on top of a real gun and fire it during Overwatch and/or instead of your main gun when within 12" against very soft targets.  If you have a tac squad with a grav-cannon you're planning on dropping in a Drop Pod and you want maximum versatility so the squad doesn't mind shooting whatever, having one of these on hand will let you swap to it for murdering GEQ.
*'''Inferno Pistol:''' If you're Deathwatch or Blood Angels, this is legit useful on the rare occasion you live long enough to fire it, because it performs as well as a meltagun for half the cost, but in practice you're better off with a Power Fist.
*'''Lightning Claw:''' Great at shredding GEQ, but why are you worried about getting better at that?  Inferior to a Power Fist against any heavy target for the same cost, and that's what the squad might need help punching, so generally not worth it.
*'''Plasma Pistol:''' Inexcusable - a grav pistol but worse in practice.  Hard pass.
*'''Power Axe/Maul/Sword:''' The Sword is the best of these, but they're all worse than a Lightning Claw and have the same cost, so hard pass.
*'''Power Fist:''' If you insist on taking a melee weapon, this should be your go-to: helps your squad against the targets they most need help against while only costing 5 points, rather than paying even more for a Thunder Hammer on a squad that prefers shooting anyway.
*'''Thunder Hammer:''' Slightly more efficient than a Fist provided you're hitting a target with the wounds to take the damage and the save is 3+ or worse.
</tab>
</tabs>

*'''[[Intercessor|Intercessor Squad]]: CORE, 18pts per model.(Jan 2023 Update)''' The bigger boys. Have become the go-to for a high damage output Troop choice with their buffs and Stratagems. Comparing the Rapid Fire version to Tacticals, you get an extra point of AP and 6" of range on their guns and +1A in melee for just 2pts more per model, but critically, if you switch to their assault weapons, you get ''3'' shots out to 24", not 2, and it doesn't matter if you stand still or not. With A2, plus Shock Assault, plus an A3 Sergeant who can be equipped with a power sword, chainsword, power fist, or thunder hammer, they aren't hopeless in a melee. Even basic Intercessors come with a bolt pistol sidearm, so they actually get three S4 AP0 D1 attacks each if they're locked in melee. In addition, one bolt rifle can slap on an auxiliary grenade launcher, buffed to let you fire a grenade up to 30" as an assault weapon instead of a grenade weapon, meaning you can fire a grenade at the same time as using the bolt rifle. 
**Specifically, what Intercessors are ''best'' at is 5 Assault style rifles on the squad plus a grenade launcher, meaning the whole thing spits out 15 S4 shots and 3.5 S3 ones, and you either leave a chainsword on the sergeant, or kit him out for better melee, depending on your chapter/build/plan.  The whole thing is 105 points; in terms of comparing to Tacticals, their most comparable build is ''also'' 105 points, with 3 bolters, a storm bolter, and a grav-cannon, netting you, at 24" (assuming the unit stands still), 10 S4 shots and 4 S5 AP-3 D1-2 shots, making the Tacticals better against harder infantry (like MEQ) if they stand still or are in close range, while Intercessors don't care about moving and are pretty dedicated to murdering chaff.  Neither unit is ''great'' at melee, but the Intercessors are better.
***If you're wondering, against GEQs (T3/5+Sv) the tacticals average a total of 4.74 wounds per turn. The Primaris deal 3.70 wounds with bolt rifles or 4.44 wounds with auto bolt rifles, plus an additional 0.78 from launching a frag grenade, for a total of 4.48 and 5.22 respectively. While this reaffirms that if you want to clear chaff you should go Primaris (especially given their drastically improved melee effectiveness), it's a surprise to see that the auto bolters still need the grenade launcher to outcompete the firstborn, and that the bolt rifles lose outright.
***Against enemy MEQs (T4/3+Sv) the shooting mathhammer lands ''decisively'' in the Tacs' favour. For the Primaris, both regular and auto bolt rifles average 1.67 wounds/turn while the stalkers land 2.22, with an additional 0.26 from the frag grenade launcher, meaning your most efficient loadout deals an average of ~2.48 wounds/turn. For the tacs, three regular bolters plus the storm bolter dish out just 1.11 per turn, but the grav-cannon is simply ''monstrous'', dropping a massive 2.96 wounds/turn for a total of 4.07 wounds - and unlike the Primaris, who lose damage output linearly with casualties, the tacs can suffer 80% casualties while losing less than 30% of their damage output. The grav-cannon is so powerful, in fact, that even if shooting at single-wound MEQs, the mathhammer still favours the tacs over the primaris.
<tabs>
<tab name="Bolt Rifle">
The bolt rifle is the basic small arm, with 30" Rapid Fire 1 S4 AP-1 D1, and is the only one that benefits from Bolter Discipline. The bolt rifle is a surprisingly niche choice this edition; against GEQs it's comfortably outcompeted by the auto bolter, and against multi-wound MEQ and up it's comfortably beaten by the stalker. The only time you'd really pick it is against single-wound MEQs, as the stalker's damage is overkill and so deals lower damage overall. The auto bolt rifle does break even with the bolt rifle on damage but costs more, so is less efficient.
</tab>
<tab name="Stalker Bolt Rifle">
The stalker bolt rifle has harder hitting rounds, being 36" heavy 1 S4 AP-2 D2. This makes it the pick of choice against other marines and bruisers like Tyranid Warriors, but you're sacrificing both Bolter Discipline and the fact that you'll only benefit from Devastator Doctrine, which only works on Turn 1 unless you're Dark Angels or Deathwatch. Of note is that it's only your best pick against MEQs if they're multi-wound; otherwise, its reduced fire rate means that your DPS is actually lower than either of your other options.
</tab>
<tab name="Auto Bolt Rifle">
The auto bolt rifle is 24", Assault 3 S4 AP0 D1, giving it increased rate of fire and mobility in exchange for reduced range and armour piercing. Surprisingly, the reduced armour piercing doesn't make a huge difference; its rate of fire gives it the best performance against GEQs, and against MEQs it breaks even with the regular bolt rifle, though both are beaten comfortably by the stalker.
</tab>
</tabs>

*'''[[Intercessor|Assault Intercessor Squad]]: CORE, 17pts per model. (Jan 2023 Update)''' Similar to the guys above, but built for melee rather than ranged combat - naturally, this means they're much worse when actually assaulting, since they can't even carry assault weapons. AP-1 chainswords mean they butcher light Infantry with four attacks on the charge, and an 18" AP-1 bolt pistol can threaten Infantry at medium range as well. The Sergeant can swap his pistol for a plasma pistol or hand flamer, while being able to replace his chainsword with a power sword, thunder hammer, or power fist. Note that unlike their Firstborn cousins they can't take jump packs, so you'll have to make sure they can get into melee first. 
** {{W40kKeyword|Black Templars}} love these guys, but {{W40kKeyword|White Scars}} prefer regular Intercessors with auto bolt rifles and a Sergeant kitted for melee.

*'''[[Intercessor|Heavy Intercessor Squad]]: CORE, 23pts per model. (Jan 2023 Update)''' The biggest boys in Gravis armour. Gravis makes them very durable, giving them T5 and W3, on top of a higher damage output.
** Quick comparisons: The standard five-man Heavy Intercessor Squad is 140pts, giving you fifteen T5 wounds and five S5 guns. With those points, you can have seven Intercessors (fourteen T4 wounds and seven S4 guns) or eight Tacticals (sixteen T4 wounds and inferior guns, but you can swap bodies for special/heavy weapons to keep the the same pts cost). Per-point, they're less efficient than tacs with a stormbolter/grav-cannon against absolutely everything, and less efficient than light intercessors against everything provided they choose between auto/stalker and frag/krak correctly; however, against T4 and T5 they do have the highest average damage. Given the extra wound and point of toughness, this makes them more viable as damage-dealers as they're likely to stay on the table longer and so get more shots off.
** At T5 and Sv3+, they're extremely durable and likely one of the best objective holders for their points cost (Custodes with storm shields will obviously hold better, but cost staggeringly more). Most armies' S4 anti-chaff will bounce off, while weapons purpose-built for gibbing Tacticals/Primaris tend to be D2 or Dd3, meaning twice the shots to bring them down and plenty of wasted wounds; three D2 wounds will kill three normal Intercessors, but only one Heavy Intercessor. 
*** Iron Hands, Raven Guard, and Salamanders Heavy Intercessors will be extremely efficient regarding durability as opposed to the other Gravis units. 
** S5 weapons and the ability to add one flavour of Primaris heavy bolter means they're well-suited to camping objectives, particularly as per-point they're shitty melee fighters likely to get bogged down in assault. However, don't be afraid to throw them into melee! If your opponent ''knows'' they're shitty brawlers they might not be expecting it, and their stats mean they're great for bogging down enemy units, giving your other units time and space to move.
<tabs>
<tab name="Heavy Bolt Rifle/Heavy Bolter">
36" rapid fire 1 S5 AP-1 D1 is a decent balance of all stats, while also affected by Bolter Discipline. If the squad is equipped with heavy bolt rifles, one Heavy Intercessor per five can swap their heavy bolt rifle for a heavy bolter, which is heavy 3 and D2 in comparison.
</tab>
<tab name="Hellstorm Bolt Rifle/Hellstorm Heavy bolter">
30" assault 3 S5 AP0 D1. The range and Assault classification makes moving irrelevant unless you're trying to move and advance 5" + d6" towards an objective, thus meaning that the -1 to hit could be worth it. Hellstorm heavy bolters are 30" heavy 4 S5 AP0 D2, and thus can't be fired if you advance to make full use of the hellstorm bolt rifle, but you can always walk or even stand still - 3 shots at AP 0 is better than 2 shots at AP-1 against save 4+ or worse and breaks even against 3+, and while walking the rapid fire competition doesn't get bolter discipline, so all told, the Hellstorm rifle is usually better than the Heavy rifle.  Similar logic applies to the heavy weapon choice: going from 3 shots to 4 and AP-1 to AP0 is better against saves 5+ or worse and breaks even against 4+.  All of these numbers proceed by 1 under an AP buff, like from the current doctrine: the assault rifle is better than rapid, even while standing still, against 3+ or better, breaking even at 2+, while the heavy hellstorm becomes better at 4+, breaking even at 3+.  However, it bears noting that no doctrine applies to both rapid fire and heavy or assault and heavy at the same time. 
</tab>
<tab name="Executor Bolt Rifle/Executor Heavy bolter">
42" heavy 1 S5 AP-2 D2 is the Fuck Marines option, but you lose accuracy on the move, Bolter Discipline, and fire rate at short ranges (making you more vulnerable to Deep Strikes and units getting close to engage in melee). The executor heavy bolter is a 42" heavy 2 S5 AP-2 D3 monster, with a decent chance at dealing the finishing blow to bigger targets as well as outright killing Terminators.  Significantly, this is the only option that lets the entire unit be buffed by a doctrine at once - the whole unit will get better AP on your first turn.
</tab>
</tabs>

*'''[[Infiltrator|Infiltrator Squad]]: CORE, 20pts per model. (Jan 2023 Update)''' The in-between of Scouts and Intercessors, filling the role of Vanguard troops that are excellent at area denial. They're armed with marksman bolt carbines, which are essentially boltguns that auto-wound on unmodified hit rolls of 6. They have Concealed Positions and their Omni-scramblers prevent Deep Strikes within 12" (thus nullifying Deep Strike charges and flamers). One model can be either an Apothecary-Cadet to reduce the damage of the first failed saving throw each turn to 0 (remember, your opponent is free to shoot you with low-damage weapons first to pop this, then switch to high-damage ones) or a Comms Specialist to count as always being in range of a Phobos Captain and/or Lieutenant aura if those models are on the field (still waiting to deep strike, in a transport, etc will still not work). With MEQ resilience, they're better speedbumps than Scouts, and now that Scouts are Elites for some reason, you have no alternatives. Like Intercessors, they can struggle to be more than keep-away units and pregame objective holders, using the Smokescreen stratagem for protection.
**The ability to guarantee rerolls on to-hit and to-wound rolls of 1 from anywhere on the board sounds powerful. Unfortunately, the maths simply doesn't bear up; '''there is absolutely no scenario (against infantry) where Infiltrators will outdamage properly-equipped tactical squads or intercessors, even assuming those squads have no reroll support and are forced to suffer movement penalties to their Heavy weapons.''', Against 3+ or 4+ GEQ and single-wound MEQ, auto bolters plus frag grenades dish out more damage than marksman carbines; against MEQ, TEQ and Gravis-EQ stalkers plus kraks do more damage. Tacs with a storm bolter and grav-cannon come out on top in every circumstance except versus GEQs; but if the tacs don't move, they're better than the Infiltrators against those GEQs too. This isn't even damage-per-point, by the way, this is just raw damage - per-point is even worse, even assuming the captain and lieutenant are free (it's not like you wouldn't take them anyway). Unless you're very explicitly taking them for the omni-scramblers or have a way to get exploding 6s (see below), you'll get better results for cheaper from tacs or intercessors. Maybe it does better if paired with the +1 to hit from the Vanguard Spearhead, essentially making it a full re-roll to hit, but even in that case the +1 is doing the [[Lion El'Johnson]] share of the work.
**Now we said 'against infantry' for a reason, the auto sixes to wound mean that if your fighting something like an Imperial Knight or Leman Russ. . .You should be using proper anti-tank weapons, but if you have to have infantry dump shots into a tank, then the Infiltrators do a better job of it then other troop choices, but not enough to replace the job of a proper anti tank unit.
***Effects that trigger on 6 to hit stack, e.g. with the Imperial or Crimson Fists chapter tactic a 6 to hit means an auto wound plus a rolled wound. With access to full re-rolls, such as a nearby chapter master (the comms array won't work) or phobos librarian, you can re-roll successes in the hope of more sixes. Ordinarily this is only worth it if you only wound on a 6+ (regardless of re-rolling 1s or all to wound), but if you increase to BS2+ (such as from a Chaplain shouting at the unit, or Crimson Fists shooting at something outnumbering them), it's also worth it on a 5+ to wound unless you can fully re-roll the wounds as well. Stacking +1 to hit, 6s to hit auto-wound, and 6s to hit to generate a hit that rolls to wound is so powerful that it's ''always'' worth re-rolling successes, regardless of the target's to-wound roll.
**Their omni-scramblers' deep-strike denial stacks with the default 9" minimum for deep-strikes, meaning you can deploy them up to 21" away from other friendly units and still deny all the space in between. Combined with concealed positions and the reduced map size of 9th edition, this can allow you to deny an astonishingly large portion of the board to your opponent.
***Leaving them this far from your main force ''will'' get your dudes killed, so bear in mind you're paying 24pts/model for a sacrificial unit. However, doing this can give you a huge advantage; holding up a Genestealer charge or whatever for even a single turn can allow them to more than earn their points back by proxy. Your standard Bolt Rifle's range is 30", but most armies' troop guns are 24". For the cost of a single sacrificial squad and with careful deployment, there's a very real chance that your opponent won't be able to shoot the meat of your army on the first couple of turns at all - which can be invaluable if going second.

*'''[[Incursor|Incursor Squad]]: CORE, 18pts per model. (Jan 2023 Update)''' The jack-of-all-trades of Vanguard Space Marines, able to infiltrate, provide support at range, and hold their own in melee. Occulus bolt carbines ignore cover and all ranged attacks these guys make (which means the carbines or a grenade) ignore hit/BS modifiers, making them the bane of enemy units that rely on cover saves or hit penalties for durability. Their paired combat knives give them AP-1 in melee this edition, and they can also buy a single Haywire Mine to dissuade enemy charges with d3 mortal wounds (three mortal wounds if it was a Vehicle) 1/game.
** Worse than Assault Intercessors for stabbin' (you don't get +1A from chainswords or the heavy bolt pistol to fire in melee), worse than Intercessors for shootin' (unless you're targeting cover/hit modifying units), and worse than Infiltrators for denyin' (no omni-scramblers). But they are the only one that can do all three jobs at once, [[Tau|so out fight what you can't out shoot]] and[[Ork|out shoot what you can't out fight]].