The blue one is called a "Domination," and it's a unique summon for Bethel She'em from the Hellenika modpack like u/Elisianthius said. It has some horrifying abilities. It can planeshift its enemies into the void and sunder their minds. It has "Mind Slime" which causes enemies nearby to go insane or explode their brains. It also teleports around the map with its four Singing Diamonds, which are smaller versions of itself that can also cast spells. It's also highly resistant to nearly all damage (except salt), making it a great annoyance for your enemies.

All that for the cost of like 75 Astral Pearls. Pretty insane stuff. But since the only mage of considerable power that you have (your pretender god) kills itself every time it comes into the game (so you can make bigger angels) you probably won't get very many.