Soundblaster

One of his main goals (and the reason he became evil) is to get revenge on Soundwave for beating him in a beat boxing battle, Soundwave sacrificed himself to stop Tarn, meaning even if it wasn't by his hands, Soundblaster got what he wanted in the end and is still roaming around and potentially destroying more planets.

Pure Evil Wiki: Soundblaster (Destroyed entire planets just because he lost a beatboxing competition)

Near Pure Evil Wiki: Future Mr. Ross (Attempted to destroy the entire universe just because he lost a volley ball game tournament)

Inconsistently Heinous Wiki: Luan Loud (SmokyCrstall11 Creepypasta) (Violently killed her own family (including her baby sister) just because Luna didn't spend all her time with her)