B:TB&tB season 3 episode 1 "Joker: The Vile and the Villainous!" Directed by Ben Jones.
A laboratory in Atlantis. For some reason in this episode the writers wrote Atlantis as if it's inhabitants breathed water instead of breathing air under giant domes. I have no idea why they did that just for this one episode.
"Batman: The Brave and the Bold" ™Warner Bros. Animation.