The idea behind this mod was to make getting valuable resources harder, and encourage building bases above ground.
Also, to allow the scaling of mobs by distance for use in exploration / adventure mod packs.
Allow spawning of certain mobs below a set y level regardless of light levels.
Difficulty scaling of mobs by y level.
Difficulty scaling by distance from 0,0.
Difficulty scaling by dimension.
Mobs get increasingly better armor and weapons the more difficult they are.
Most options this mod adds are configurable in the config.