I like the flavor of it, and I'm sure that Adamzero would go on forever about how this can make the game last infinite turns. In actual gameplay it's probably degenerate in certain cases, and base mercy is basically useless with no attack squares because it can only do its combo, and from a limited distance.

For example, imagine using mercy to resurrect an enemy's pawn in front of your Soulkeeper over and over again to get more ghosts.