Heldrake
Heldrakes are a type of Daemon Engine utilized by the Chaos Space Marines in Warhammer 40,000. Introduced in Sixth Edition, they were immediately the center of a deliciously skubtastic debate.
Heldrakes are giant, metallic, fire-breathing, Chaos dragons/jetfighters. They used to be regular Space Marine aircraft, but they've been warped by the power of the Immaterium. The pilot(s) remained trapped inside, only to have his body consumed and his soul bound to the daemonic machine; in fact, the Heldrake's roar is actually the amplified screams of the former crew. They travel trough the Warp clinging to their warband's ship, before soaring into battle like a bat out of hell (quite literally), and wreaking unholy havoc (Word Bearers approvedTM).
This is, of course, really awesome fluff, but it's from Phil Kelly, so that's not exactly a surprise.
The model itself has a FATAL-size anal hole. Many fa/tg/uys find this absolutely silly, although it is based on an old Epic 40,000 model, so...
Crunch-wise, Heldrakes were hilariously overpowered (nowadays considered merely pretty good), in a book that is generally pretty weak. In fact, Heldrakes are considered pretty much the only thing keeping Chaos Marines competitive nowadays. Fielding more than one (sometimes even only one) Heldrake in a game is the fastest way to have your opponent bitch about the only thing in your Codex that can keep you on the board and have him ragequit. If you field three or more you automatically are That Guy.
A Heldrake also appears in C. Z. Dunn's novel Pandorax, where it shrugs off at least sixteen direct missile hits, three point-blank twin-linked lascannons, and about a hundred tons of falling rocks. As if the things didn't have enough durability (see below) without an extra helping of plot armor.
19 Months of Cheese
For all of 6th Edition, H-Drakes were considered mainstays in everyone's top five cheeseiest units. And looking at it in the context of the times, it's not hard to see why. Its cheese was famous, almost memetic, like how Pyrovores are terrible. It all stems from three major factors:
Durability
First and foremost, it's a flier, so your options for hitting it are already limited. More to the point, it was the first flier of the edition to be designed AS a flier (as opposed to Stormravens, which were designed as skimmers). The early meta had no idea how to deal with fliers, so anyone playing against a Heldrake wasn't prepared for it. Nobody had Skyfire weapons except Guard players with Hydras, and Hydras were falling out of favor since they couldn't hit ground targets very well anymore.
But just hitting the flier was the first step. You also had to get past front and side Armor Value 12. Keep in mind this was before 6th Ed. Tau, so almost everything that had Skyfire was S7. It's also a Daemon Possessed vehicle, so it had 5+ invuln. And unlike other fliers, it got this for free, whereas other fliers could only Jink if they were willing to snap-shot the following turn. To ice the cake, they gave it It Will Not Die, so your hard-earned efforts of finally hurting the thing could be all for naught.
Damage Output
By default it has a Hades Autocannon, but nobody took it because it could also get a cheap yet amazing weapon called The Baleflamer. Good lord, just the Baleflamer! S6 AP3 Torrent, a weapon designed specifically for killing MEQs that coincidentally doesn't care about the bird's lackluster ballistics skill. Did we mention the Baleflamer was considered turret-mounted? Yes, it didn't matter where you actually positioned this thing, it could fire in any direction, letting the Heldrake deliver miss-free, cover-ignoring, multi-model devastation without even paying attention to where it's going.
It could also Vector Strike D3+1 times at S7 AP3 Ignores Cover, just by moving over you, so MEQs (remember, Vector Strike became AP2 in 7th ed, which also reduced the amount of hits to one against ground targets) and vehicles aren't safe either. And as a flier it can Vector Strike pretty far in a single turn, picking and choosing whatever it wanted, and always hit side armor on S7, so any attempt at clever positioning was basically wasted.
Long story short, you have a weapons platform that can threaten almost everything your opponent could throw at you (and completely ignore the few exceptions), but was especially geared towards destroying MEQs en masse.
More Than The Sum Of Its Parts
A flier is one thing. A loadout that can hurt almost any unit type is manageable. After all, we keep things in reserve all the time, and aren't Torrent weapons supposed to flush you out with near-impunity? But the Helchicken was like a guide book on how to design something with no real weaknesses.
As a flier the Heldrake could hide in reserve at the start of the game, completely off the board, then get a free Vector Strike before Interceptor weapons could fire at it. Unless you hid everything against your table edge, it was guaranteed to hurt something. In the high likelyhood that it was still alive after Interceptor (which not all armies had to begin with) it could then put a Baleflamer template pretty much anywhere, including on the former passengers of whatever vehicle it just Vector Struck to death. With a 36 inch move and a further 12 inch Torrent in a turret there was basically nowhere on the board that was safe from a Heldrake once it rolled to come in.
Basically the Heldrake was the ultimate exercise in "anti-zoning", and was so amazing at it that in completely ignored one of the 40K meta's more fundamental tactics: screening. Everything else in the 40K series could be blocked off, could be tarpitted, could be bogged down or hidden from, or at least be given a token level of resistance to annoy the controlling player. But the Heldrake? It just shouted "Fuck you I'm a dragon!" and flew right over everything right on top of whatever you wanted to kill. It could hurt anything, nothing could hide from it, and very little could hope to fight back in any meaningful way. It had the hat trick, the golden trifecta of an overpowered unit. Hell, it even negated its own intended weaknesses; as a Daemon vehicle it was supposed to suffer from BS3, but neither Vector Strike nor Torrent gave a shit.
Lastly, just to leave a bad taste in the mouths of cheap entitled neckbeards, the Heldrake was a brand new vehicle. You can bet your sweet ass Heldrake kits were expensive. Naturally you have everyone losing to these things accusing GeeDubs of making their traditional overpowered army of the months scheme. And when it was discovered that 6th Ed. Chaos Space Marines weren't exactly a god-tier codex without the Heldrake (sweet euphemism, it went from, depending on which Chaos God you swore allegiance to, unspectacular (Nurgle) to absolutely terrible (Khorne) if the player didn't fork out money for at least one Drake), you had the CSM players (rightfully) joining in too.
And Then, 7th Edition
With the arrival of 7th Edition and the corresponding FAQ, the Heldrake took several massive hits in its brazen demon balls that might throw it down from the mighty spire of cheese it so proudly dominated before. First, the rulebook changed the rules of the Vector Strike USR to only do one AP 2 S user hit on normal troops, while enemy fliers take D3 instead, and after that, the recent FAQ nerfed the Heldrake by removing the turret rule to the flamer weapon, so it now has to shoot from the tip of the weapon, i.e. the head of the drake. While this might not make it unusable, it does nerf it to more logical levels for a flyer. This did also create the retarded/awesome new tactic of putting something under the very tip of a Heldrake's wing in the movement phase to be able to vector-strike it and target it with a baleflamer. This basically means that Heldrakes now spend their days going around the place and decapitating people with their fucking wings.
Additionally, the meta has shifted quite a bit with the new edition. Everybody has their own fliers of varying effectiveness now, and any army can get (and is more or less expected to take) some sort of anti-air, the more effective of which (Ork traktor kannons and Tau broadsides) simply laugh at those that would cower at the sign of a heldrake.
Even further, towards what is now the end of the 7th edition Cycle, pretty much everyone now knows exactly how to deal with flyers. Both flyers and Skyfire have proliferated to such an extreme that they created their own take on Mutually Assured Destruction. If someone brings a flyer, it'll kick ass, but not if the opponent has literally any kind of anti-air. On your opponents side, if they have anti-air, it'll be wasted if the opponent doesn't have a flyer, but on the plus side it means all flyers are now completely useless. This has left the game now in the rather unusual state of nobody taking flyers at all, and nobody taking anti-air either.
8th Edition
With how much GeeDubs is hyping this as a new edition with actual balance for once, it'll be interesting seeing what becomes of the Helturkey. Luckily the leaks have already told us. The removal of flamer templates means flamer weapons simply get a certain number of automatic hits; the Baleflamer specifically deals D6 auto-hits at an 18 inch range (S6 AP -2, 2 damage). It Will Not Die has been buffed game-wide (and given about six different names), so Heldrake automatically heals a wound at the start off its turns. Speaking of wounds, it's T7 12 wounds 3+ (for comparison, that's a Predator profile with +1 wound), also 5++ as before. Vector Strike is gone, replaced by just giving the turkey a melee profile (WS 3+ S7 AP -1, D3 damage). It's only downside is that it does not have Hard-to-hit like certain other fliers, so the enemy is hitting it on full ballistic skill (it can also be charged by ground units, but tarpitting doesn't really work against it). All this for 138 points. (Plus the claws...)
Alternate take 09/04/18 - Due to the lack of hard to hit, and the sheer randomness of its damage (1d6 auto hits on the flamer, 1d3 damage per claw), Helturkey looks a lot scarier than it actually performs and its role has generally been relegated to hunting squishy FLY keyword units and hit-and-running heavier infantry. Too, at 185 points (with a Baleflamer, because no one wants to have an Autocannon hitting on 5+s) a Defiler or Wings&Axe Demon Prince can generally do the same job. The only difference the Helturkey has from these is that you can pretty much guarantee your opponent is gonna empty everything they have into it on round one, which gives the rest of your army notable breathing room. If your looking for a scary bullet sponge with a lot of potential (but only on a good day), the Helturkey is your boi.