Mewtwo VS Shadow the Hedgehog - S3-E6
Revealing mistake: During Shadow's Super Shadow transformation, half of the background becomes a green screen.
Death Battle (2010)
1 revealing mistake in season 3 - chronological order
Starring: Chad James, Ben Singer
Samurai Jack VS Afro Samurai - S5-E9
Continuity mistake: After jumping right behind Jack, Afro attempts to stab him, and Jack avoids it. When Jack turns back to face Afro, it looks like there is a bit of distance between them, despite Afro being right behind Jack in the exact previous shot.
Nightwing VS Daredevil (DC VS Marvel) - S5-E12
Nightwing: What are you?
Daredevil: Better. (00:16:10)
Trivia: This was the first episode of the show with actual voice acting.