Cast Retaliation on Epic Butcher, and he gets charged by a unit of standard melee models. The first enemy model attacks, and before the attack is resolved, Retaliation goes off, and Butcher gets an attack. But since he has Homocidal Maniac he has to make a melee attack against everything in his melee range, possibly killing the whole offending unit before they get to strike (aside from the first one).
Thanks to Pressganger Devilsquid for this handy tip.
