Ravenor. After spending a good portion of the action stuck in his life-support hover chair incapacitated and subject to the abuse and threats of a psychotic lowlife who attempts to crack open his sealed environment with an axe, he reacts the instant he gets his psychic powers back. Let's just say Mr. Axe-Happy becomes no more than a red smear on the nearby bulkhead....
Not to mention once Ravenor's Berserk Button gets pressed after Mathuin dies.
Bounty Hunter Lucius Worna gets his while he's fighting a genetically enhanced opponent. He grabs the man's arm, and bites his implanted blade off with his bare teeth. After properly incapacitating his target, it's heavily implied that Worna cuts the target's face off.
When Nayl is fighting a shapeshifter and quickly gains the upper hand, the shapshifter, in desperation, morphs into a likeness of Nayl, hoping that it will distract him. Nayl just grins, says "Fancy that", and then snaps her neck without batting an eye.
In Ravenor Rogue, Magnificent Bastard Molotch, just by sitting in a restaurant, devises several ways to bring the entire galactic sector to its knees with a single vial of poison.
Potentially even more impressive, is the fact that the Tyranids wouldn't appear for another 300 + years, so Molotch laid a deadly trap that he should not have even been aware that existed. Maybe also a point of how powerful the Door was.
Eisenhorn acquires another one in the short story Thorn wishes Talon, included in the Ravenor omnibus. Ravenor's entourage is pinned down by a Chaos Dreadnought, a sticky grenade (their last one) has just failed to do anything, and Eisenhorn just walks up to it, trailing frost through the air (indication that he's using his psyker abilities). He then cuts it in half with his sword, in one stroke. Killing a dreadnought is awesome. Killing it in close combat with one blow makes this the crowning moment of the story.
Wystan Frauka, the generally shunned, despised and barely tolerated Untouchable of Inquisitor Gideon Ravenor's entourage, gets one at the end of Ravenor. Ravenor, and indirectly his entourage and the ship's crew, are at the mercy of The Dragon, an insanely powerful psyker called Kinsky. Frauka is shot and left for dead on the bridge, where Kinsky is projecting his mind in a psychic battle/curbstomp with Ravenor. Frauka suddenly wakes up. He lights a lho-stick. He turns off his power-limiting device. Kinsky's mind is dragged back into his body, powerless. Frauka simply reaches, snaps the normally hideously dangerous man's neck like a twig, turns his limiter back on, and falls over. This single act frees Ravenor's own immense psychic power to swiftly take down every remaining villain on the ship. And the ship firing on them.
Ravenor's last resort in any dangerous situation is to 'wear' one of his colleagues - that is, to psychically possess their body and use all of his power and expertise in their place. Given that Ravenor's actual body is horribly crippled and he has spent decades on a life support system, it is frightening how often his skills quickly (often, brutally) end a fight that his entire team of hardened mercenaries consider dire, when called upon.
And in Ravenor Rogue? He wears two people at the same time. While one is unconscious and the other actively resisting his influence. While simultaneously controlling his own body. Which is also operating the psychic-equivalent to a pair of gatling guns. Against an enemy that he has never met before. Which later turns out to be one of the most dangerous enemies ever faced by mankind; the Tyranids.