Isn't that guy on that eye... ...familiar? - Pawns Of Cthulhu spawn message.
The Pawns Of Cthulhu (Mobilizer & Cleric) are Bosses fought in the Lunar Age mode and the Boss Rush.
Mobilizer is a large eye covered in metallic goo. In phase 2, Mobilizer has a striking resemblance to Reintazer's 2nd form. In Phase 3, Mobilizer moves much quicker than his 2nd phase. He also shoots metal shards and spawns Demon Eyes. If he isn't defeated when Cleric is dead, he will despawn and spawn The Twins.
Cleric is similar to the 1st NPC you have when you start the game. The only difference is that his skin tone gets darker when he is hit. Like Mobilizer, he has 3 phases. Each doesn't make his appearance change, but it does make Cleric faster.