Board Thread:General Discussion/@comment-27907368-20160514064034/@comment-26347196-20160515042448

Yossipossi wrote: It's actually unknown how much HP Sans has. His ATK is 1 and his DEF is 1, but where does it say HP? Ah, there's the part.

I think there's a small theory that Sans has a huge ton of HP, if you ccombine the fact (from the Snowdin innkeeper) that sleeping will restore you HP past the limit and the fact that Sans sleep a lot during the course of his life here.