I feel like the fandom is really sleeping on the potential of Skoodge and Keef interactions. Just imagine:
Skoodge comes to earth and pretends to be Zim's cousin, or an unrelated stranger who for some reason seems to have struck up a friendship with Zim. Keef thinks since he and Zim are friends that he's inherited Skoodge as a friend by proxy, and Skoodge just goes along with it. They get along great, both thinking they're best friends with Zim, oblivious to how much Zim despises them both.
Keef sees the new kid Zim is hanging out with and gets insanely jealous that Zim's allowing this guy near him but keeps Keef at a distance. Keef was there first!
Dib recognizes that Skoodge is another Irken and shows him the same hostility and suspicion he directs toward Zim. But Keef misreads it as Dib being in love with Zim and jealous that the new guy is stealing his man. So, like any good friend who just wants his friends to be happy, he tries to get rid of Skoodge. Not necessarily permanently. I think it could be really funny if he was following them around, trying to knock over cans of paint or something to embarrass Skoodge or force him and Zim apart and then arrange for him and Dib to be alone together so Dib can confess his feelings.
Keef thinks he's friends with Zim and Dib and that Skoodge is an interloper taking Zim away from them, so he sets out to get rid of Skoodge so it can be just the three of them again. But Skoodge is just so nice he ends up winning Keef over and they both realize that Zim and Dib are jerks who don't appreciate them. So they ditch them to go be best friends together. Skoodge even reveals that he's an alien to Keef and offers to whisk him away to have space adventures and ride space bunnies and drink space sodas together. Maybe Skoodge even has a full redemption and joins the Resisty with Keef while Zim and Dib stay on earth carrying on being miserable with their dumbass rivalry.
