Yibb-Tstll enjoys a considerable amount of power and is said to be able to see all things in the universe at all time, and even to see through time and space, making it so wise that only the omnipotent Yog-Sothoth can surpass it in terms of wisdom. Yibb-Tstll is even once called "The Patient One".

Yibb-Tstll's blood is alien and can be utilised as a weapon known as "The Black", which takes the form of black snowflakes that stick to a victim and smothers them.

Often envisioned as an immobile dark mass of tentacles with a deformed head, detatched eyes and large bat wings under which countless Nightgaunts suckle from innumerable breasts (heavily implying this monstrosity is either female or (more likely) a hermaphrodite).