Wirewolves are these creepy Daemon Engines used by the forces of Chaos, and encountered during the Sabbat Worlds Crusade. Despite being the same size as a man, these things are scarier than walking in on a Haemonculus skull fucking his latest victim, as they are very fast, very tough and capable of tearing a man in half without a second thought. Despite the name they usually do not resemble wolves, being more a daemon powered man made of thin pieces of warped metal, with the wolf part of the name coming from how they hunt and run down the people they are hunting. They are capable of transforming their forms to some degree though, and as such this means they are Motherfucking Chaos Transformers!
Wirewolves spend most of their time hanging around on specially fashioned metal gibbets, where they look like creepy ass scarecrows. These hanging racks have had chaotic rituals performed on them, which has made the space between reality and the Warp so thin that the Immaterium could finger its way through to real space when the Wirewolf needs to be activated. The Wirewolf would absorb chaotic energy while hanging here and so would be soaked in the stuff, allowing a daemon to possess the frame and control it when needed. They were used as a kind of riot police force, a really brutal and scary police force, that could be summoned by wandering "glyfs" (sentient Chaos runes) when the local population of a planet started to step out of line. Once awoken, they were completely uncontrollable and would start to kill anything in the area and in the way as they ran towards their designated target.
However the big downside to Wirewolves is that they expend their energy very quickly, and are usually only able to be active for a few minutes before they are forced to return to their hanging racks to recharge their warp energy. They also explode (like all good deamon engines do) when they were damaged enough, detonating in a torrent of Warp energy and screaming pissed of daemon, as well as flash shadowing any poor bastard within a 5 meter radius.
Being able to partially change its form, Wirewolves can make almost any weapon it can forge in a near instant, from burning hot blades that can disintegrate people with a single cut to potentially a crude warp-fire thrower. The quick adaptability, combined with the strength and speed of the Wirewolf makes it lethal to even Space Marines, and an absolute horror for light infantry as they can rip through a squad in seconds.
They were encountered by members of the Tanith First who were on a mission on the Chaos held world of Gereon. They managed to defeat the Wirewolves that were summoned against them, with a combination of las-bolts, dumb luck and divine intervention. Not even joking on that last point, surgeon Ana Curth destroyed a Wirewolf with some flasks of blessed water (that was brought to counteract the effects of Warp while being stuck on a chaos tainted planet), which does kinda make sense as Daemons are capable of being destroyed and seriously hurt with holy objects. Who knew that the best way to take down a Demonically powered, killing machine was with a Squirt-Gun full of holy water.