Age of Sigmar/Tactics/Old/Order/Ironweld Arsenal

Literally every single Warmachine from Dwarfs and Empire model range folded into one army. Given their lack of other units outside 2 relatively fragile Heroes, it's clear that this is to be combined with other armies like the Freeguild to 90% reform pre-Grand Alliance Empire or Dispossessed for Dwarfs.

Warscrolls

Heroes

• Cogsmith: Dwarf/Duardin Engineer. Comes with a Dwardin Pistol and a Grudge Raker (D3 -1 rend attacks). Can repair a single warmachine within 4" for 1 wound.
• Gunmaster: Human Engineer. Has more decent ranged options than the guy above with all of his ranged weapons being rend -1 and he hits on 3+, but is utterly pathetic in close combat.

Warmachines

• Steam Tank Seems too random and weak for its reputation at first, until you realize that with his ability you re-roll ALL of his random values, which makes it very threathening both at range and in close combat, specially against units with 10+ models. Get one or two Mages with the Lore of Life close to this thing, heal it each turn so its performance doesn't decay, and you won't fear anything. After all, who needs monsters when you have TANKS?
• Cannon: Ah, the famous cannon. If 3 Crewmen are within 1" of the Cannon, this thing fires 2 shots that do D6 wounds. If you're incredibly lucky, you just dealt 12 wounds. With an Engineer within 1" you re-roll hits. As always, an excellent unit.
• Helstorm Rocket Blaster Fun to use and scary as hell when you realize how much damage it can potentially do with D6 damage with a full crew. Uses Ork mentality of MORE SHOTS IS BETTAH BOSS as they hit on 5+ so i would recommend taking 2-3 of them if you want to take them at all and stick a master engineer in the middle of 3 guns to use his funny but unreliable rule that lets all missed shots hit another unit of your choice (within 10") on a on a D6 roll of a 6. Be wary of the minimum range however as they can't shoot at anything within 10" The crew also has a peculiar rule that says they add 1 to the to hit rolls when firing all salvos at the same target, but as they can only come in a unit of 1 gun carriage they can only shoot at one target anyway? So by that logic i would assume they get this bonus all the time but that doesn't make sense so if anyone would like to point this out that would be greeeaaaat. The rules for attacking state that models with multiple attacks may split those attacks amongst different enemy units within the attacking model's range. So instead of splitting the shots amongst different units, you gain +1 to hit against an enemy unit that you really don't like.
• Helblaster Volleygun: You decide whether you load 1 deck, 2 decks, or 3 decks. For each deck you decide to load, you roll a D6 to determine how many shots you get. However, any doubles rolled means the Volleygun jams and cannot fire that turn. A Human Engineer within 1" can allow you to re-roll ALL of the dice.
• Gyrocopters: Well, the Gyrocopter is supposed to be a mobile gun platform and it is. It's mobile, it's pretty tough, only they sort of forgot to give it a good gun. It's Brimstone Gun pours out three Irondrake shots (woohoo). It's Steam Gun is potentially hilarious. You pick an enemy unit and get one shot for every model in range, though that range is 6", so you'll get at best one salvo before you get stuck in melee. However, three of them stuck in melee can erase entire units with their Steam Guns. They're also some of the most overpriced models GW has ever made, so have fun getting those three. Once per game, they can also drop their bombs, which will, on average, result in one mortal wound per Gyrocopter. Yeah. If you have 3 with Steam Guns, they're hilarious, resulting on average in one wound for every model in range, but otherwise, skip, dorfs have way better war machines than this.
• Gyrobombers: A tougher Gyrocopter who forgot to put a good gun on it because it was too busy fitting bombs to its hull. Its gun is pretty much four Thunderer-shots. It can also drop bombs every turn and they're better than what the Copter has, dealing D3 mortal wounds instead of the two individual rolls. However, since they only hit on 4+, you'll need at least two to have any sort of reliability for your bombs. The biggest shortcoming of the Gyrobomber is its 12" movement, which while fast for Dwarfs, isn't too great, especially since you must be able to completely fly over the enemy unit and clear it by 3" to be allowed to move over it. Sure you could run, but what about your awesome gun? Also, the way the bomber works usually leaves it stranded way off from your main force, far away from any buff your dorfs rely on for survivability.

Organ Gun: The gambling gun. Its profile is at first underwhelming, being D6 Irondrake shots, but the trick is that you can decide to shoot it up to 4 times. Then, you roll a D6 and if you roll under the number of times you fired it (so, 1-3 if you shoot four times), it jams and you don't fire at all. At peek efficiency, it fires 4D6 Iron Drake shots, up to 24 and still 14 on average, but that gives it a 50% chance of not firing at all. In an Engineer is closeby, you can reroll this jamming test, giving you a 75% chance of it working at peek efficiency and an 88% chance of working with 3 barrels. Yeah, Engineers are awesome.

Allied Armies

• Freeguild: Arguably the fluffiest and best choice. It's already defensive and ranged, and this just gives it more horde-killing and monster-killing options.
• Dispossessed: See above.