Is there a name for a comic relief character that temporarily becomes highly capable? This is a trope that I've seen sometimes in comic books. I haven't seen it in prose fiction yet. Sometimes, we see a character who provides comic relief become highly capable for a single issue or chapter. Examples include a few Donald Duck stories, or Lambik from Suske & Wiske (Spike and Suzy). This phenomenon usually happens when the story requires a strong character to get something done; the character who provides comic relief is a logical choice as they can afford to be somewhat inconsistent. Is there a name for this trope?

The most related trope would probably be Crouching Moron, Hidden Badass, when a minor character with no apparent skills turns out to be a super-secret ninja-assasin in disguise.

A subtrope of this is Took a Level in Badass, which is seems to be pretty much what you're looking for. This is when a character pretty much suddenly develops a cool power, though it can be temporary or permanent.

Also could be Beware the Silly Ones, where a goofy villain turns out to be your worst nightmare. The Undertale genocide route boss is a good example of this. Beware the Nice Ones and Beware the Quiet Ones are also similar.

Warning: All but 2 links are TV tropes links. Click at your own risk...