The undead miner! It will be a zombie wearing a miners helmet( which you can craft with 5 gold bars and a torch ) that glows. It will( the undead miner ) have 25 hp and it will always hold an iron ...
You should add new ores like : Copper , Tin , Silver , Platinum , Tungsten , Lead and Bronze. The power should be Diamond > Platinum > Tungsten > Iron > Silver > Lead > Bronze > Gold > Tin > Copper