Honestly, I was kinda confused by the cast at first because there's a lot of 'em, but the absolute core duo is the twin Dream Gods, Dream and Nightmare. They're like the central axis everything spins around. Dream's the cheerful, optimistic one trying to spread positivity, while Nightmare is his corrupted brother drowning in negativity and trying to spread that instead. Their eternal conflict drives most of the big arcs.
Beyond them, you've got their 'gangs'. Dream's got the Star Sanses, which includes fan-favorites from other AUs like Blue and Ink. Nightmare commands his 'bad guy' crew, often called the Nightmare Gang, which features heavy hitters like Killer and Horror. There's also Cross, who's got a super complicated loyalty thing going on. The comic does a deep dive into all these guys, their messed-up backstories, and why they fight. It’s less about good vs. evil and more about broken people reacting to trauma.