Thought Lurkers are half-existing entities only present in the Imaginarium.
Thought Lurkers are created from the accumulation of forgotten memories, or thoughts, which is why they can also vary in size, appearance, and power.
The power variability can vary from near powerless to omnipotent^infinity, since if a group of entities thought about omnipotent entities, those dead thoughts could accumulate and create a powerful thought lurker.
How they survive
Thought lurkers can only survive if an entity thinks about something that is not completely fictional, therefore, they can half-exist.