Memento Vitae
Death in Minecraft is a curious things... You lose your life, your items, and Experience. Yet, you return not even seconds later ready to start again or claim what is lost. Your items are tangible things that were crafted or found for use... but experience is something else. You gain experience from Crafting, Killing Mobs, and Breeding animals. It is the essence of your characters life and as such should be a much harder thing to truly lose.
Memento Vitae prevents XP from Dropping when a player dies. Any experience that would drop is instead given back to the players new form minus any loss determined by the config.

