This is copied from My Curseforge page, " https://legacy.curseforge.com/minecraft/mc-mods/forge-simple-zombie-apocalypse" This Project is Likely will be abandoned by me. But you can copy it and maintain it in your version as long as you credit me

Update 2022/05/31: Im currently working for improved and Polished version of this Mod with much more content(relatively speaking) with 1.18.2 release. might be released in future as different mod because its little different than what this mod does

WARNING: THIS MOD MIGHT LAG OUT YOUR PC! because theres so many zombies spawning in certain conditions! I Dont Recommend using this mod in low end pc!!!

In This mod. simply swarms of zombies will attack you!
You can Change The Probability of spawning by using command /zombieprobability <number 0~100>
don't set it to too high or tps will go down, initial value is 5(%) and its already chaos and so many zombies will spawn

Zombies Mostly Spawns In Night, And The amount of zombies is insane.(depending on /zombieprobability settings) Zombies Mostly spawn in surface

Zombie Spawns EVERYWHERE when its night or dark!!!! even in the end dimension and it will be CHALLENGING (to your PC)

/doeszombieburns <true/false> - This Command apply to newly spawned zombies and it doesn't apply to already-existing zombies initial value - false
/zombiespeedlevel <number> it determines level of speed effect applied to zombies. This Command apply to newly spawned zombies and it doesn't apply to already-existing zombies initial value - 1
/dokillallzombiesday <true/false> if its true. it will /kill zombies during day no matter what
in 1.12.2. some features are unsupported and cannnot be used

Makces