Clumps
Clumps created by jaredlll08 is an optimization mod used in this mod pack to help optimize everything about the game.
It is:
Clumps groups XP orbs together into a single entity to reduce lag when there are many in a small area. On top of this, it also makes the player immediately collect the orbs once they touch the player, so you are not stuck with a bunch of orbs in your face.