Use:
/function mobrain:start
#To Start

/function mobrain:stop
#To Stop

/function mobrain:uninstall
#Run Before Removing

/function mobrain:zcommands/resetdata
#Resets the Datapack

tag @s add spec
#Mobs doesn't spawn on the player with tag spec



Customizations:
scoreboard players set cooldown dataMobRain (integer)
#Sets the cooldown for spawning Mob. By Default set to 60

scoreboard players set mobMode dataMobRain (integer)
# Modes# 1 = hostile only# 2 = all normal# 3 = all including boss

scoreboard players set mode dataMobRain (integer)
# Modes
# 1 = rain all player
# 2 = rain random player

Extra:
Random: Adds a way to get pseudo random number

/function random:uninstall
#Before removing