- Smash Bros HP. Play D&D as normal but add your damage up. When your damage passes a threshold, save or die. Roll d100 and roll over your damage total or die. Do this every subsequent instance of getting hurt.
Maybe use the old HD as the threshold. Like, wizards start testing at over 4 damage. Or alternatively save every time they take damage, screw the bookkeeping. - I'M THE FUCKING DADDY system. Standard HP, except they are now how you hit things. Gamble your HP as dice. Each HP spent lets you roll a die, but keep the same number as you usually would. Rolling to hit, spend 3 HP, roll 3d20 and pick the best one. Spend 8, roll 8, keep 1 and so on. All violent action takes energy.At 0 HP you are at the whims of the enemy. They can automatically kill you, or the DM can have them do something else, like kidnap you or chop your arms off.
Damage works like normal, but use HP to roll the dice.
Probably wanna increase HP pools a bit. - DAMAGE DICE EXPLODE. The d4 knife is now interesting
Unsure death is fun. Having a sense of impending doom is fun. Knowing you can take a couple of shots is too comfortable. Turning your life resource into currency is exciting.