Undertale but Damage is Permanent

This mod makes it so that all damage you take cannot be healed back, by essentially causing all sources of damage to also hurt your max HP.

The logic of gaining LV has been tweaked for this mod, instead of setting your HP to a specific value, each LV up grants you an additional +4 max HP on top of whatever you already have. As such, True Pacifist is by far the hardest route to do with this mod, since you don't get any of these 'heals', so Neutral or Genocide is most likely the way to go if you value your sanity. Dying only sets you back to your last save point with whatever HP value you had when you saved, although you may need to reset if you have too little HP to reasonably continue.

Tubbsy came up with the idea for this mod, and he even managed to beat the Genocide route with it without dying a single time, here is his documentation of the journey:

Keep in mind that this mod is ONLY tested for the Genocide route, though I believe it should work fine for most Pacifist/Neutral encounters, excluding Omega Flowey (probably).