Episode 86 of "Angel"
s04e20 Sacrifice

Angel and the gang escape from the hotel, decide to hide out in the sewers in order to escape from Jasmine and her followers. While walking around, they encounter a large group of teenagers. They tell the gang about a bug-like creature dwelling in the sewers. Wesley is captured by the creature and takes him to it's lair, where it is piling up bodies for a sacrifice. The creature tells Wesley that Jasmine was originally their God and they loved her first. She had a name that had power over her, but only one creature knows it. The creature lives in Jasmine's dimension. Wesley asks how they get to the dimension, but the creature tells him that there is no oxygen in the dimension and the only way to get there is by using his orb. Angel finds Wesley and brutally kills the creature. Wesley picks up the orb and smears blood on it, opening a portal. Since Angel is the only one who can live without oxygen, he jumps in...