SPOILERS FOR UNDERTALE AHEAD
The hardest boss in Undertale is the most surprising. Laid back skeleton Sans has been holding back, and the only reason you’re alive is because he made a promise to someone.
This stat block mechanically represents his abilities in a D&D world situation. He’s incredibly powerful, with the ability to use Reverse Gravity, a 7th level spell, at will. Size limits don’t apply to this, so even the largest threat is still going to get affected by this spell. His only real protection is his incredibly high pool of hit points and his ability to use shortcuts to escape.
If you’re fighting sans in D&D, you probably did something wrong. He is Karmic Retribution incarnate. And if you can’t SAVE and LOAD, you’re screwed.
Sans was an interesting character to me, and can be seen as an archetype. He’s a lazy friend with incredible power, who only interferes when absolutely necessary. He knows that when faced with people who can control time, he doesn’t stand a chance, so why bother? You can create a Sans-like NPC in your game.
If deities that can alter reality or change time exist, there’s not much you can do against them. The NPC has incredible power, akin to a demi-god, but knows that any major actions they take are meaningless. They become fatalistic.
When the NPC can’t sit aside any longer, they finally step in. They have a strong ideal that propels them to act, even with knowledge that it may not matter. They’re going to give it their all. And you better hope that they’re not fighting you.
Here is the statblock for Sans! I hope you enjoy it.