Ultra HardCore, where you dont regen hp naturally and if you die you're out of the game.
People use that feature (/gamerule naturalRegeneration off) to do UHC matches, where people will gather resources within a time then fight to death. Last one (team) standing wins.
Golden apples or potions are used to regen, but those are way too gold intensive for a modded survival, thus the requirement of something different.
As mr10 mentioned, no pvp and no "out of the game", just the survival aspect of UHC. Unless we want to do some private matches.