请为《探险活宝 第五季》写一段简要的内容简介，包括主要角色和故事背景等，最好不要过多剧透，结尾可以是开放式的。
Finn and Jake chase the Lich through a dimensional portal where they meet Prismo, who tells them that the Lich wished for the extinction of all life. This leads Finn to wish that the Lich "never even ever existed.