This is a PROTOTYPE version with more to come.

The basic premise of Hearts Challenge is you begin your game with reduced health and for every advancement you make you gain some life. If you die at any point, you are penalized by losing some (or all) of the life that you gained from advancements. It could be considered semi-hardcore because there's a definite penalty for dying, but your world and everything you built is not lost. It also creates a mission for your world: chase advancements.

In this version, you start with 1 heart (2 HP). You gain half a heart (1 HP) for each listed advancement that you achieve, and you lose a full heart (2 HP) whenever you die. The advancements don't reset so eventually you will stop being able to earn back what you've lost if you die.

To run this datapack, load it into a new world. It will set time to noon, turn off day/night, weather, and mob spawns to allow you to be ready to get started. Click in the menu to get started, time is set to zero, mob spawning, day/night, and weather are turned back on, and your health will be set to 2 HP.

There is a bug in Minecraft where sometimes current health doesn't show correctly. If this happens, closing and reopening the world will fix it.

This datapack does work on servers!

Advancements that earn a half heart are:
Getting an Upgrade
Acquire Hardware
Diamonds
Isn't It Iron Pick
Suit Up
Not Today, Thank You
Cover Me With Diamonds
We Need to Go Deeper
Hot Stuff
Enchanter
Eye Spy
Return to Sender
Hidden in the Depths
A Terrible Fortress
This Boat Has Legs
Spooky Scary Skeleton
Local Brewery
Who is Cutting Onions?
Remote Getaway
What a Deal!
Hero of the Village
Bullseye
Bee Our Guest
Sticky Situation

Future work:
1) Fix the start menu so it doesn't require commands
2) Make it easier to swap custom advancements in
3) Functionality for randomized advancements
4) Different game play modes -- teams, free for all, etc as well as customizable start, gain, and death penalties
5) Fast play using quick advancements vs multi-day play with more difficult/tedious advancements
6) Win condition, if you finish all the advancements and beat a specific one last (like kill the dragon), you win the game and you can die without resetting your health.

If you're interested in the full "mini game" version, you can check out the plugin that I wrote for Spigot. It was written for 1.15 and only works on Spigot servers. There's more detail of the full game version in the description. That will give you a better idea of what this can grow into.
https://www.spigotmc.org/resources/kaleys-hearts-challenge.77830/


I'm actively working on this datapack to make it a lot more customizable. There should be more updates to it in the coming weeks.