One of the proposed mechanics for the Black Knights Faction from the Goblin Artisans Black Knights design challenge.

This is Larry Paulsen's Overthrow mechanic.

This mechanic fits my desire for there to be a saboteur theme somewhere in the set.

This triggered a couple of times, including once for the opponent while under the influence of a (((Geass to Betray))). Seems fine, but probably not enough to base a Black Knights mechanic on, especially if creatures are small enough that this would need multiple creatures to get through.

(On the other hand, that would mean attacking with, say, two 2/2s the opponent would really want to block one of them, which forces creature combat to happen providing a venue for the combat tricks... hmm.)