Revealing mistake: When Clouseau is floating out of his apartment in his costume, in several shots you can see the shadows of the chimney behind him in the sky, indicating this was shot in a studio.
Revealing mistake: When Clouseau strikes Cato on the back of his head with the shinai it's actually just hitting the doorframe to his right with Cato flipping forward on cue.
Continuity mistake: Clouseau's clothes go back and forth from being wet to dry during his numerous and failed attempts to get into Dreyfus' castle and falling into the moat instead.
Continuity mistake: When Dreyfus goes crazy again he's completely soaked, When he's chasing Clouseau he's suddenly dry.
Answer: Just Invisible. Besides the fact that his eyeball and eyelid remain intact and in the same position, he returns in a full, visible form (possibly in a film logic borrowed from Looney Tunes cartoons) in the next Panther film.