Complex sentence: In "Chosen", Buffy and the other Slayers go into the Hellmouth to fight the Turok-Han; in the end, all of them are apparently killed, including thousands by the amulet that traps Spike.
Split into simpler sentences: In "Chosen", Buffy and the other Slayers go into the Hellmouth itself to fight the Turok-Han. In the end, all of them are apparently killed, including thousands by the mystical amulet that entraps Spike.