Scaling Mob Difficulty is a simple utility mod that gradually increases the difficulty of hostile mobs as the game progresses by increasing health/damage, as well adding armor-piercing capabilities to mobs later on. After day 3, undead mobs will stop burning, as well.

Customizing the mod with commands:

/scalingmobs

  - health (deals with the scaling of hostile mob health)

  - damage (deals with the scaling of hostile mob damage)

  - piercing (controls how much of mobs' attacks ignore armor)

  - mode (choose between linear progression or exponential progression)

Also has configs!