'' I'll steal your Heart and Eat it in Front YOU!!!''
Hate!Sans isn't considered a skeleton, as a being made of pure hatred he has no physical form so his apareance looks like the form of a sans made of black smoke. He was born from the pure hatred acumulated inside a sans from an AU in which the human wouldn't quit reseting, he held a grudge against the human and the monsters, since resets made them forget all about it but sans couldn't forget the resets. That grudge became bigger and unbearable as his hatred mixed with his determination and magic created Hate!Sans, who started to blind him with such rage that Sans started to murder unconsciously, he even murdered the human and took their soul for himself so that the human wouldn't be able to reset ever again.
Hate started to spread over the underground, after he was finished he went back for the human soul. Sans didn't want to give the human soul so Hate threatened to kill his brother if he didn't give it to him, Sans gave the soul to him but that didn't stop Hate from killing his brother right in front of his eyes. Hate killed that Sans too so he wouldn't be a problem later for him, his plan was to destroy the barrier and spread his hatred over the world and then leave it empty of any feeling other than his own. How? Hate feeds off hatred from people, this comes with a consecuence for the person, after their hatred is consumed, they are left with a trauma that makes them become empty shells without any feeling left, as if they didn't had a soul anymore.
His personality is a bit bipolar, one minute he is calm and relaxed the next he's acting sadistic and stressed. He enjoys the company of Dreamtale Gaster and loves talking with him. He doesn't need to eat normal food because he feeds off hatred, he's never actually had fun since his job is kinda hard, but he manages to put in some time for himself.
Hate!Sans appears to be a Phantom of a skeleton and is untouchable and invulnerable to damage, only when he wishes to because he can let his form become solid if he wants or if he feels comfortable enough. He appears to be kinda foggy and has a completely black look to him making camouflage except for his eyes which are red and white.
Hate's body is made up of 15% magic, 20% Determination but it may grow if he's battling someone, 60% hatred in the form of fog or smoke, which makes him untouchable and invulnerable to damage, but his eyes are the 5% that is solid.
Since he's a Phantom that means he can posses the living and make them do things they wouldn't normally do.