In the episode Frozer, Ladybug and Cat Noir are getting Ice Forms! With ice crystal patterns and skates! And in another unnamed episode, they get Underwater Forms with fins and everything. Here's my theory:
Master Fu said that the Miraculous Book contained many spells and incantations that can grant new powers to the heroes. So, I think he's gonna transform into Carapace and activate the new forms by chanting the spells. He said he could partially decipher the code, so yeah. Anyone else think this?