Soulbound

When you die, you leave behind your soul, which can be recollected by punching it.

If you do not have a soul, your max health will be set to 12 (6 hearts) and you will gain permanent Weakness, Slowness, and Hunger until you get one back.

You do not have to recollect your own soul, you could kill someone and take theirs if you want to. You can also steal other souls by punching it whilst holding a Glass Bottle.

Souls in Bottles can be crafted with 7 Ghast Tears, 1 Soul Sand, and 1 Glass Bottle.

I recommend pairing this with Keep Inventory so this acts as a new challenge on death, instead of just making it harder to get your stuff back.

(Made using MCBuild)