Apophis is a loner when it comes to the Egyptian pantheon: None of the Egyptian gods want anything to do with him. However, some of the other serpent gods at school hang out with him sometimes. It's not easy being green (or black, or any other color, when you're a giant serpent…).
We're not sure if it's Medusa herself who befriended Apophis, or if it's just the snakes on her terrifying head. Or maybe Apophis is trying to recruit this Greek monster maiden to help him in his fight against Seth, since everybody she looks at turns to stone?
Loki's son, the Viking sea monster Jormungand, is almost as big as Apophis, and at least as mean. Unfortunately, Jormy's not great for conversation, since he has his tail stuffed into his mouth until the end of days. (So Apophis better get working on that.)
Typhon, the scariest thing in all of Greek mythology, is so similar to Apophis that some people wonder if they're the same guy, er, evil serpent. (Never seen them both at the same time, have you?) But we know that Zeus locked Typhon up in Tartarus—the clan makes special field trips to visit their buddy in prison.