What will pose a challenge is a Techno-Shaman. Read the description of Distort Function, realise that a suit of power armour and a storm bolter or power sword are two mechanical devices, and that a Space Marine doesn't get an opposed test to resist this power.
It actually makes me chuckle to imagine a group of space marines standing around going "hurrrrr" as the techno-shaman wanders in between them and just merges the entire unit into some Akira-esque abomination. Don't get me wrong - RAW, it's a hilariously broken power if you can actually get it off. Just wave your hand and permanently destroy every single piece of gear on every character within range, no save. Heck, use it on someone's bionics, kill him instantly, or at least leave him crippled for the rest of the mission. No save.
But Range: Psy Rating x2 meters says that unless yours is the stealthiest Rak'Gol in history, or manifests next to the PCs out of a cloud of GM fiat, I don't see that happening very often. Parties without Forbidden Lore (Xenos) don't count, for the same reason parties that cram meltabombs up their noses and detonate them don't count - you obviously can't win if you commit suicide.