Reaping Enchantment

The Reaping enchantment would be an enchantment that could be placed on any weapon.

What it would do is cause it so that when you get xp, instead of going directly to your xp bar, it goes to your weapons enchanted with Reaping. If you hit a mob with one of said enchanted weapons while your xp is in this state, it deals one extra damage per one xp in your weapons. The xp used to deal damage in this way is then expended, rather than going to your xp bar, and if you defeated the mob, any xp that wasn't used to defeat it remains in your weapons. One xp would move from your weapons to your xp bar per second. Reaping would conflict with Mending. (If this paragraph was confusing, try rereading it carefully until you understand. If you don't get it, I'll summarize it for you: this enchantment lets you sacrifice xp to deal extra damage.)

One remaining question you may have is how this handles bosses. You defeat them and suddenly have hundreds of xp in your weapons enchanted with Reaping, and killing mobs is suddenly too easy for a few minutes. I say, don't bother with fixing that issue. You're still choosing to take mob drops instead of xp, just like any other time with this enchantment.