Blood Slaughterers are another Daemon Engine of Khorne devoted into having the most obnoxious name possible with the word blood in it. Seriously I dare you come with a more stupid name than Blood Slaughterer, well okay GW already did that with the Bloodsecrator.
Slaughterers are larger than a Dreadnought, and look like a hunched, overgrown tick that has fed itself on way too much blood and metal (Seeing as how most ticks feast on blood, oh GeeDubs you sly motherfuckers). Slaughterers are armed with a multitude of monstrously large claws and blades as well as Impalers making it a formidable weapon of war on the battlefield.
Hilariously back in 1st Edition and early 2nd Edition the Blood Slaughterer was a small Daemonic robot of Khorne on two wheels rather than the humongous robo-tick of doom. The Slaughterer was one of Khorne's daemonic machine creatures of iron and brass. It was protected by a daemonic aura, making it harder to kill than usual. However, with the advent of the Codex: Chaos (2nd Edition), the Blood Slaughterer was phased out of the Chaos army list only to make a return in 2015 by Forgeworld.
On the Tabletop
Generally, this particular Daemon Engine has been very killy since its inception. They're tough, fast, and dish out loads of punishment; Forgeworld only made them better at it while giving them a better model, TBH.
The Slaughterer back in the early days of WH40K was daemonically possessed and subject to a bloody frenzy as it travels swiftly on iron-bound wheels while carrying twin-linked Heavy Bolters, a Chainaxe and a Lash of Khorne. The Lash was a powerful energy whip, crackling with energy, the iron claws at the tip of each whip dripping in corrosive venom. Other than that, not much is really remembered about the Blood Slaughterer from 1st and 2nd editions; they were phased out at the end of 2nd and sat out three rules cycles until Forgeworld resurrected them.
From 4th to 5th edition, Chaos generally got squared in the junk with the nerfbat in 40K; it seems however that Forgeworld didn't get the memo and decided to crank out some nasty units for them in 5th with the advent of the Siege of Vraks - one such unit was the humble, resurrected Blood Slaughterer of Khorne. They only got more powerful throughout the editions and not even 8th Ed's reset button could dampen their damage output.
So how did they play? Like a fucking MURDER TRAIN, that's how! They had an outrageous amount of S10 attacks bypassing armour at WS and I of 5, thanks to having 5 attacks plus rage, giving them another D3 attacks on the charge. They weren't glass cannons either, sporting AV 13/13/11 and being immune to shaken and stunned results; oh and they could fleet! Those alone are scary but they were vulnerable to both shooting and kiting by faster units; however, Forgeworld gave them the option to take Impalers at the expense of one of their CC attacks and close combat weapons. Basically, it was a half range krak missile that always hit on a 4+ (useful, considering the Slaughterer's BS 1); additionally, any wound to a monstrous creature or penetrating hit allowed you to drag the model D6 inches towards the Blood Slaughterer. Oh yeah, and they could be taken in vehicle squads of 3, amplifying their brutality handily.
Basically, they were amazing; still, they could still get kited by jetbikes and the like because of the requirements of 5th Edition Rage rules, but whatever they touched would be guaranteed dead! Also, if you played daemons during this harrowing time to be a daemons player, you could take these and they had to deep strike like the rest of your army, thus helping you bypass some of the major flaws of the unit; essentially, playing Daemons was the tax for fielding this freight train.
6th & 7th Editions
Really, they only got better. 6th Edition Chaos Daemons, long since the butt of jokes from 4th and 5th, were a playable army and the Blood Slaughterers power was jacked up sufficiently to compensate. Everything from the previous edition carried over save for the requirement to charge whatever was closest and now they had to pass a 2+ to ignore crew shaken and stunned results. Then, they got two new special rules tacked onto their profile: Daemon of Khorne granted them furious charge (which did nothing) and a 5++, buffing their survivability; and then they got Deep Strike, and not just for Chaos Daemon armies, either. Next to Obliterators, they were the go-to deep-strikers in 40K being roughly the same size as a dreadnought and frighteningly more powerful. They were also one of the few things in the game now that could effectively wind up in close combat on their turn after deep-striking due to a hilarious quirk in the rules; the strategy was effectively to strike near a MC or vehicles, impale it and drag it towards you, rip it to fucking pieces and then sweeping advance into the next victim. Dynamite!
7th edition didn't really do much to them; they got added into some formations and detachments, which were already broken but 7th edition was just borked all over.
The great 40K reset button made sweeping changes to the rules; they now sport a toughness, wounds, an armour save and a movement value as was standard to all vehicles in the game. The Slaughterer lost the ability to be taken in squads of three and to deep strike while getting shuffled into the Fast Attack slot. For that exchange, it received a beefy new stat line: M10, T7, WS3+, S8, W10, 3+ Sv (with 5++) and A6 base clocking in at 180 pts.; it also comes stock with its impaler which you can drop for another slaughter blade for free. Speaking of, those blades hit at S+2, AP-3 and deal 3 damage per hit - OUCH! The impaler isn't as spectacular as it used to be - its basically a S8 blade attack at a 12" range that allows it to charge an extra 2 inches if you wound a vehicle or monster, which is still decent. Finally, like all vehicles and monsters, the Blood Slaughterer has degenerating stats, whereby its S, M and A all decrease if it's taken a certain amount of wounds; at worst, it can move 6", has S6 and 4 attacks... which is still amazing, really!
The big change are to this thing's special rules: it gets an extra 2 attacks if it's fighting infantry and cannot run away if within an inch of infantry (note, falling back is a thing that happens in 40K more frequently now), advances a flat 6" without rolling any dice, can regenerate 1 wound at the start of your turn automatically and if it dies, roll a D6 - on a 6, ever unit within 6" takes D3 mortal wounds!