Azmuth arrives, takes back the Ultimatrix (calling it an "inferior copy"), and gives Ben the completed Omnitrix he has been working on for years.

Vilgax tempts Ben to use Dagon's power and Ascalon to "wipe evil from the universe," but Ben ultimately chooses to use the power only to restore the humans transformed into monsters.

While often referred to as a Season 2 special, this episode is widely considered the darkest in the series. "Danny Phantom" The Ultimate Enemy (TV Episode 2005)