Assigns mobs a level based on distance from (0, 0), by default this is every 100 blocks distance. It then increases the health and attack of mobs based on the following formula:
(Base + Flat * (level - 1)) * (1 + Rate * (level - 1))
The values for Base, Flat, and Rate are all configurable and the defaults are 20 (Base), 2 (Flat), and 0.0075 (Rate).
The mod also adds an overlay showing the mob's level and health: