* heya kid, so, uh, this contains spoilers. i suggest you to play the game first.
1 HP.
This is one of the few theories that might as well be true, although there may be a few proof that debunks it.
One reason is seen in the Inn (Snowdin, near the Entrance and just to the right of the SAVE point). It is stated there by the inn owner that for a bit of G, you can sleep in the Inn. Sleeping increases your HP.
Now, how exactly does this relate to sans?
Sans is known to be one who's extremely lazy, and is said by Papyrus that he sleeps a lot, normally when he's at 'work'.
If HP = Hit Points = Strength, that can explain how Sans is actually rather strong in the Genocide route. He is undoubtedly one of the strongest Main Bosses in the game, too. Demonstrating attacks such as:
However, pay attention to what happens towards the end of the battle- lo and behold, Sans falls asleep! Why is this so?
This is seen when you check Sans during your battle:( something among the lines of: )
* 1 HP and 1 ATK.
* Can't keep dodging forever.
* Easiest enemy.Throughout the battle, Sans actually dodges the attacks aimed from the player (assumed to be Chara in the genocide route), however this tires him out. This happens:
Sans sweats after a bit of battle. There's another theory surrounding this, however. Though, as Sans keeps dodging, he gets tired after a while to the point he sleeps at the end of the battle [after throwing the player 36 times against the bullet box, depleting 1 HP per hit]. Sans' HP likely depleted each time he dodges, as if you notice, some of his attacks weakened around the battle though the difficulty still stays ( doesn't really include the GB spam before he falls asleep ).
If I were to use HP = Hit Points = Strength, Sans would probably have more than the Player at LV 19 (HP: 92) as he sleeps quite a lot. This strengthens his attacks. At the start of the battle, he mentions: gee, i wonder why people don't use their strongest attacks first. If Sans were to use his strongest attack first, that depletes his HP the most.
Thus, the player has a huge advantage in a way. Imagine you were in a battle, you and your opponent are mages. Your opponent uses their strongest attack first, this depletes their MP (magic power) much quickly and falls. In game-context, MP will heal, but I will not be using game context. So, consider that. Will you have an advantage against your opponent?
Going back to Sans actually sweating in battle, this shows his tire. Even though this is seen with Papyrus, he is sweating due to his nervousness. His HP is to it's lowest point, thus, he is not able to fight for too long. Sans' battle lasts for 22± turns.
However! Look at what Sans had done when he fell asleep, but the player had chose the MERCY button instead of FIGHT:
After sleeping for a while, he was back to his normal state, no sweating and all. He brings up bones in the bullet box, killing the player (together with the KARMA damage).
Sleeping heals.
This, probably concludes my theory. A bit confusing, so feel free to ask me questions!