Cartman is very greedy and selfish, killing Clyde in The Walking Dead and causing Kenny's death by shooting himself and knocking Kenny into the horde. Cartman is also non sympathetic, showing no remorse when his friends die. He also, joins Craig's Rebels in Riot.
Stan: Cartman and Stan don't interact much, but when they do, it is rarely positive. Cartman faked caring about Stan being alive during Riot, and later was present when Craig killed Kyle and Kenny, leaving Stan to bleed to death. He is later killed by Stan.
Kyle: Cartman and Kyle do not get along, possibly due to Cartman's arrogance and behavior.
Kenny: Cartman and Kenny don't interact much, mostly in The Walking Dead, notably when Kenny brutally assaults Cartman for shooting Clyde and getting him killed by the zombies. Kenny points a gun at Cartman's head, preparing to kill him, but shows sympathy and gives him a second chance. Later, Kenny and Cartman are trapped on a unstable roof, and Cartman shoots himself in the mouth with his shotgun, causing Kenny to also get eaten.
Lenny: Cartman doesn't interact with Lenny much, and he doesn't care about him, and even fought with him during Unexpected Change.
The Walking Dead
Scary Campfire Stories
Kyle's Birthday Short
Lunch Fight Short