A caged, ice-cold entity Carl carries as a tattooed third eye — it begs to take him over, and freezes what it gazes upon when he opens it.
The Eye of the Bedlam Bride is a malevolent captive entity Carl carries, normally a tattoo caged behind a 'third eye' on his chest — though while he is transformed into a dachshund it relocates, hidden, to the center of his dog forehead. It is sentient and covetous, whispering to Carl in the middle of the Desperado Club mimic ambush — 'Let me, Carl. Let me take over' — and he must firmly refuse, insisting it stays trapped and that he is in control, while it purrs that it will be 'here when you need me.' When the Mitch mimic lunges to devour dog-Carl, he reflexively opens the Eye and it freezes the adolescent Shadow Mimic solid: Mitch shudders, sparkles as if filled with glitter, and screams 'No. Don't do this.
It's too cold. It's too cold!' — held helpless until Princess Donut finishes him. The episode shows the Eye as both a hazardous passenger straining at its cage and a devastating frost-weapon Carl can loose at need.
Elle warns him that keeping such secrets 'is going to bite us on the butt.'
A caged, eye-shaped entity worn as a tattoo — on Carl's chest normally, on his forehead in dog form — radiating a killing cold when opened.
A caged, cold-wielding entity riding Carl as a tattooed third eye, straining to possess him and freezing foes when unleashed.
Also appears in books you've already read — spoiler-safe to their endings: