How HH Works: Each time you die, you lose 2 Permanent hearts, and the hearts next to your user change color too based on how many hearts you have.
/sethearts [User] [Amount] Set that player's amount of Hearts [0-20]
/last [User] Just like in the official series, it will replace the player's heart next to his user with a "⚠️" of the same color of his heart amount, if they have this, no matter how many hearts they have, next time they die they get automatically banned.
/heartless [User] make the player's hearts Black, making him immortal but capable of taking damage.
/immortal [User] Make the player's hearts White, making it so that he's immortal and can't take damage, even if in survival.

This project attempts to add the features of heartless horizon in a papermc plugin.