A non-physical link between Carl and Katia that survives being pulled apart and binds him into her dream.
When Carl and Katia take their dream potions together, both go a little loopy, and Carl feels something strange: as if he had been wrapped in plastic his entire life and for just a moment the plastic was gone. He describes popping open like a tree whose bindings have suddenly been cut. His reach is not far, but it is clearly beyond what it is supposed to be.
The two reach forward and touch hands. Edgar yells and Imani separates them, but she only separates them physically. A second connection remains between Carl and Katia, and that is what binds him into her dream. During the same expansion Carl brushes every mind nearby, catching emotion from Mordecai, Rosetta, Edgar and Bucket Boy, and far more than emotion from Imani and Katia. He believes he will forget most of it when he wakes, and reflects that although the dungeon lives in their heads, it does not read them this deeply, or if it does it cannot understand, having never been human.
No visible form; inside the dream it manifests as Carl and Katia's hands intertwined and fused as though surgically affixed.
The accidental link that puts Carl inside Katia's dream and briefly opens every nearby mind to him.