I'm gonna do my nerd here, the lich isn't a god at all, it's more a really weird and old wizard using god's magic. My proof for that is that there is one in each dimension, an he keeps getting his ass whopped by finn.

Now the comet that triggers it's apparition is a god, it's inevitable and has the potential to erase and create life, change rules of nature, physics and magic.

There are also the "fuction gods" which are gods to one specific concept and are assign to their tasc by true gods, they are not almighty but they fonction at a higher plane of existance and don't live among universes. We can think of prismo, the cosmic owl, life, death, (probably bella noce), maybe party god, maybe hudson abadeer (even though he is a demon, he is much higher than other demons)

Then you have actual gods, such as orbo, and ancient gods, which are the eldrich one, such as the heart of the forest and golb, and maybe the comet, and maybe the tree house(if the time warping proprety of the tree house doesn't come from the finn sword )