Looks good. Never played Undertale but I've got a decent understanding of it through online osmosis, and this seems pretty accurate.
Only real sticking point is the Incite Effect. Does he ever do anything with it other than attack? If not, then I don't see any reason to require two purchases of Additional Effect.
95% of the time, his gravity manipulation is more maneuver-ish than an actual attack. He's attacking you throughout his engagement, but it's fairly clear that he actually uses it in a distinctly different fashion than his bone attacks . That being said, I think his gasterblasters and his other bone attacks are fairly similar that I'm gonna compress them down into one effect.
Also, I think he should buy the Avoidable option.
In theory this should be a Natural Weaponry thing, but I can see why you went with Incite Effect here. Mechanically it's just a better choice if you don't have Strength and want to use an unconventional skill.
PS: He's got Stealth twice.
D'oh!, yup, and D'OH, respectively.
I've never played Undertale, but if Sans simply can't be hit without being ambushed, wouldn't that be better modelled by Physical Immunity? As it is, if you have an entire party working together in stacking aspects, you'd be able to hit him in straight up combat.
Actually, this is actually further reason to leave him as is in that regard. I'd let a dedicated party stacking aspects and getting clever hit him, but definitionally, by the time you get anywhere near actually engaging the guy in combat, you have no allies (because you killed everyone). Leaving it as is is actually a fairly good way of going "if you made friends instead of trying to slaughter
literally everyone, you could have a chance against this guy (buuuut he wouldn't try to fight you anyway).
Also, gonna give him one more aspect. Can't believe I forgot it, actually.