After hours of mind-numbing coding and debugging, grueling torture, and multiple existential crisis, I bring to you the Vitality datapack! Here's what it does: You start out on one heart, and if you die, you gain a heart. However, once you die with 10 hearts, it's game over for you. The nice thing about it: unlike the X-life mod from which it derives, this datapack will work on any server/singleplayer world which is not pre-1.16. Grab a couple of friends, put this on your server, and enjoy the chaos!

I've made some recent changes to it, the only thing you should have to do now is have everyone you want in your world to play with you, then type /reload (you have to have op, or cheats enabled) and it should work perfectly. Also note that your health may look like it's on full, however once you take a bit of damage, your health will update.

Note: The video linked is not mine, it's simply a good explanation of the X-life mod. Also a great series, so there's that. I also am not affiliated with the creator of the X-life mod, nor am I sponsored by Bisect Hosting.(Although a great hosting service)