Board Thread:General Discussion/@comment-34404946-20180120072411/@comment-31147727-20180131142736

another reason this theory makes sense is that there are other instances where the coded stats are different from the in-game stats. for instance, Toriel's stated stats are 80 ATK and 80 DEF, but her attacks only do 6-8 damage (and bear in mind that we, even at ATK 1, can do 16 damage in one blow. Now, we could argue that Toriel was just holding back, and that could be valid; however, this does not explain her DEF, which is only coded at 1 (or -9999 if on Genocide). the first dummy has stats listed as 0 DEF, but is actually coded as having -5 DEF. it is like this for various characters in the game. This implies that the coded stats are different from the in-universe stats, and this would extend to Sans as well.

of course, the most obvious evidence of Sans having higher in-game stats is in the true pacifist ending, where he and all the other monsters are ensnared by vines and clearly taking damage. If Sans only had 1 HP in-game, then he would have been absorbed by Flowey immediately.