A gimmick account is meant to be comedic by using commentary.
A troll account is trying to be comedic by being an unfunny edgelord by yelling racial slurs and posting pornography links.
For example: RAUGH. He is a gimmick I made. He's harmless. He's a gimmick. eggplant.pics on the other hand, is an example of a troll alt. Posting links to what is legally defined as pornography.
Gimmicks deserve existing. Troll alts don't.