Killer is a very romantic guy, often going out of his way to flirt with the enemy.

Killer often laughs at seeing people in pain, even his teammates and people close to him. However, if someone close to him was severely wounded or hurt, he'll ease up on the jokes and look a bit worried.

Killer likes to act loud and expressive to mask his true intelligence.

He just wants to have fun with the barista.

He has a selfish, mean and playful personality and thinks he's helping out the multiverse. He steals things, raids and destroys AUs to name a few things he does. He loves to play jokes, and make snarky teases at his enemies. He doesn't get mad until things don't go his way, how he expected it to happen, or when others trigger one of his fears. And although he has a lot of hatred toward non-canon materials regarding Undertale, the ones that slightly deviate from the original annoys him the most.