The Mutant Zombie is a giant, hulk-like version of the zombie, and will be found in the night time as a rare spawn. 25% of the time, it'll be a mutant zombie villager. It attack villagers, iron golems and players without provocation.
When Killed, The mutant zombie will drop to the ground for a few seconds. it will get up with 40 health and fight you again. if you really wanna kill it. you need to light it's body on fire or defeat it 3 times in a row.