The angry zombie, a zombie who have the ability to sprint.

Angry Zombie :

An Angry zombie will be a zombie who have red eyes and a furious look.

He will be faster than a normal zombie, he will be fast like a baby zombie, do more damage, and will have more Hp than them.

Spawn Rate difficulty :

Easy difficulty : 0% chance that an angry zombie and angry baby zombie appears

Normal difficulty : 1/5 zombies are angry.

Hard difficulty : 2/4 zombies are angry / 2/5 baby zombies are angry.

Note : The baby zombie can be angry too, but they will be more rare than a baby zombie , for example they will be almost fast as the player and they will inflict more damage and have more HP than a regular baby zombies. The player will be still faster than them when he will run. It won't be a problem since it will be in hard difficulty only that the angry baby zombies appears.

Angry zombies will give the same items as normal zombies when eliminated, but they will give twice as many experience points.

If you think it's too difficult, it won't be since the zombies are one of the easiest mobs, you can still easily avoid them by escaping with blocks, the player will be still more fast than them, more you will advance in the game, more the player will literally kill them in one hit or two. The player can just sleep too or change the difficulty at any moments.