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Let's talk definitions, because I've never seen the show.
There is no trope called "Out Of Character Episode".
The key word of Out-of-Character Moment is "moment", as in "brief".
Character Derailment is YMMV, where viewers feel that a character's long-term characterization went off the rails without proper development. It doesn't really count if they misbehaved briefly and then went back to normal.
If it's longer than a "moment" and they only behave this way for the duration of one plotline (one episode, or one story arc) and then they're back to normal, you're best off looking at the Ball Index (Conflict Ball, etc.) or stuff like Temporarily Exaggerated Trait (if Darwin is prone to jealousy, but has never been this jealous before) or Compressed Vice (if Darwin has never shown any signs of jealousy before, and never shows any after this plot is dealt with).
Character Derailment isn't just YMMV by the way, it's flame bait. So you don't add it to a trope page.
Working on: Author Appeal | Sandbox | Troper Wall

I'm working on editing one of The Amazing World of Gumball episode "The Burden". Describing Darwin's attitude on his jealousy gainst Gumball and Penny, however I can't identify what trope goes proper with his attitude, if it is a character derailment or an out of character episode.
Keep in mind that throughout the series up until this point, he never showed having jealousy of Gumball having a crush and her, it's between this episode and The Bros that Darwin have this attitude.