This is a very light weight plugin that allows the user to configure the mobs health and damage between two values. Heres how it works:

A mob is spawned, if it is in the config as enabled its health is set randomly between two configured numbers
If the mob hits another Entity (player, other mob, etc) it chooses a random damage between two more configured numbers and applies it
No commands or permissions needed!

Config

effected mobs:
  skeleton:
    lower hp limit: 20 #lowest possible health
    upper hp limit: 30 #highest possible health
    lower dmg limit: 2 #minimum damage 
    upper dmg limit: 5 #maximum damage 
  zombie:
    lower hp limit: 30
    upper hp limit: 60
    lower dmg limit: 2
    upper dmg limit: 5
  spider:
    lower hp limit: 2
    upper hp limit: 20
    lower dmg limit: 2
    upper dmg limit: 5
enabled worlds:
  - world # list of worlds this plugin will alter mob behaviour

multi-world support

This plugin can be enabled/disabled on different worlds. If it becomes popular enough I may add support for different worlds having different configs.

Suggested Plugins

Combat Timer - Allows you to change the amount of time between entity attacks.

Mob Randomizer