Story starts with Sabertooth senteced to pit. Later we see sabertooth escaped the pit caught by the x-men but he easily slaughtred them later we saw he was in the pit and Doug acting prosecutor cut a deal with Creed his body remain in pit but his spirit or something roams in Krakoa. Later we saw five other mutants senteced to pit

Melter guy who is enemy of young avengers i don't know

Nekra

Third Eye

Oya

Maddison Jefries

i am suprsized see Oya and Maddison Jeffries in the pit

By the way we didn't see Toad,Orphan Maker and Nanny