XP Stains, the Bloodstains of this blocky world. 

Sick of losing all your hard earned XP in an instant?
What if you dropped ALL your XP?
What if you didn't have to worry about that 5 minute despawn timer?
Sounding familiar? Like the mod Gravestones, or maybe you prefer Corpse? I know I can't have fun without at least one of them. But those mods don't return the XP. This is the perfect addition to them.

By default, the stains work like they do in Dark Souls:
1: Die. 
2a: Get your XP Back. [Good Ending]
or 2b: Die again. (First XP Stain Fades)

Thankfully I'm not as cruel as that series, when the stain fades, an XP orb with all your levels is dropped from the stain, standard 5 minutes before it despawns. Just a bit harder to see and can be picked up by anyone. Or you could disable this "fade" feature at the risk of having XP Stains everywhere. Just like the gravestones from Gravestones.

PVP would be way more interesting if you got all your targets XP. So the configuration file has options for theft. You could make it so that anyone can pick up any XP Stain.

I know I'm not the first to do this, but I haven't seen this feature as a standalone mod. 

v2.0 (1.20.1)

XP saved is no longer 100%, but it's very close to it (more details in changelog).

Options have been moved from the Configuration File to the GameRules, this allows you to have different settings in your solo world than a multiplayer world, or even just different settings across different solo worlds, and more importantly you can change the settings in-game instantly if you have the command permission. All 3 gamerules start with "Stain" and have descriptions in-game, they can be found in the "player" section of the gamerules when creating a world. 

Added optional Glow effect for extra visibility. Enabled by default.