Board Thread:General Discussion/@comment-29947165-20160911231001/@comment-13682699-20170925013718

Sans is a magical being. His attacks all use magic to some degree. There's nothing truly special about his abilities aside from KR. It's just that because of his meta-knowledge of the game, he can use that against you (as well as dodging everything) to troll you into giving up.

He does not possess Determination, or at least in amounts quantifiable to be considered abnormal for a monster as it is still a requirement for any living being to possess some amount of Determination in order to live lest they "fall down". The only normal monster confirmed to possess unusual amounts of Determination was Undyne because she is already a naturally determined monster. Boss Monsters also have it to a certain extent which allows their SOULS to linger briefly after death before breaking as well making them naturally stronger than most normal monsters. If Sans were to ever possess Determination in amounts that would be unusual, he would simply melt like the monsters who made up the amalgamates as they were also not confirmed to naturally possess unusual amounts of Determination.

When he fights you, he is probably as determined as any normal monster can get without melting since he is honestly trying to kill you, though with his low stats and weak stamina he eventually succumbs, so obviously natural determination for a regular monster (or at least one as magically weak as Sans) can only get them so far against a being with near limitless Determination. Despite this, he still does a commendable job at stalling you out.