Grimace

Bomb Grimace
Bomb Grimace is an alternate version of Grimace that spawns Red Bombs for Isaac to use.

In the boss fight against the Tuff Twins, a couple of Bomb Grimaces will be found around the room to provide free explosives to use to defeat the boss.

Quake Grimace
Quake Grimace is an alternate version of Grimace that periodically fires a rock wave in which ever direction it's facing. It does not stop, even if the room is cleared.

Great Gideon appears to be a large boss variant of a Quake Grimace.