In Marvel Comics, the monster Loki and Sylvie face is called Alioth the Usurper. The trans-temporal entity first appeared in the 1993 comic book, Avengers: Terminatrix Objective #1. According to Marvel, Alioth is a destructive cloud that exists across all divergent realities.

Is alioth a Loki variant?

He meets Old Loki, Kid Loki, Alligator Loki and another Loki, who has a hammer. Almost immediately, Loki and the squad see a massive monster who is thrashing through the planet. Old Man Loki and Kid Loki reveal the creature to be Alioth, a monstrous creature that eats the variants and sends them into oblivion.

What creature is alioth?

A creature... you both know." Alioth is a trans-temporal entity that serves as the guardian of the Void. Alioth was created during the Multiversal War, where Nathaniel Richards harnessed and experimented on its power, becoming its master.