To Know Your Enemy, You Must Become Your Enemy
The damned tyranid queen won't stand still. I can't get a solid hit on the xenos scum unless I can dedicate a full round to attacking with my force sword, as it will simply dodge my attempts otherwise. I have to resort to my Avenger psychic power, engulfing the queen with flames instead.
Of course, I push the psychic power, because why wouldn't I. The power succeeds, but I am forced to roll on the Psychic Phenomena table. A roll of 98 on the D100 is pretty awesome, and I get escalated to the Perils of the Warp table.
Psychic Mind Swap! As the psychic flames fire from my hands, I find myself on the receiving end of them as my mind is transferred in to the body of the tyranid queen.
Now I'm the queen! The queen must be in my body, and if either of our physical bodies dies the effect will end. Perils, my arse. This is perfect. What better way to defeat the enemy than to become the enemy?
As the queen is trying to work out what to do with the puny two limbs my body has, I think I'll deep-throat this lascannon. Or maybe fling myself in to space. Or just see if I can rip out my own heart.