This datapack make minecraft zombie apocalypse.

Many Zombies
All hostile mobs nearby a player in distance 16~48 would have probability 20% to summon zombie per 7 seconds.
you can modify this chance in datapack.zip/data/zombie_doomsday/predicates/spawn_zombie.json
You need to extract this zip file to modify, if you just want to play default version, simply move zip file into folder world/datapacks/

Fast
The zombie summoned move very fast.

Summon TNT
If there are a lot of zombies togather nearby you or friendly creature, they have 6% per 11 seconds to summon a tnt (expose in 3 sec),
you can modify this chance in datapack.zip/data/zombie_doomsday/predicates/summon_tnt.json

Rush
zombie have 25% per 1 sec to rush you and friendly creature.
you can modify this chance in datapack.zip/data/zombie_doomsday/predicates/rush.json

Loot Table
The zombie will drop rottenflesh, potato, carrot, gold, iron, enderpearl, gunpowder, which perform a good compatibility with gun datapack,
which I recommend you to download with this datapack.
All the item droped by zombie will be killed per 13 sec if you don't pick them up.