I have a new game about to start up soon and one of my players wants to play a Psion. We are starting about mid-Heroic tier, so he will have the Betrayal* at-will power. Both of us are wondering how I can go about working in that power into combat, since monster allies will have just attacked another ally. He is under the impression that this would not go over very well with the enemy, but, even though I agree on a certain level, I prefer not to have a sudden shift in battle where the PC's kick back and the enemies kill off each other.
How should I handle this power when there is a group of enemies, and one up and attacks the others?
*Betrayal: a lvl 3 Psion power that can shift an enemy X squares (is augmentable) and attacks one of its allies with melee basic attack + charisma mod of the caster.