YOU MIGHT WANT TO READ ALL THIS; IT WILL HELP YOU A LOT IF YOU'RE GOING TO DO A PLAYTHROUGH 

This add-on changes all hostile mobs to have double their health and damage

True passive mobs have 50 health (true passive mobs are mobs that never attack anything period

but other things were changed other than that such as tnt, tnt is 3 times stronger, spawns fire and explodes instantly

Your health and armor now cap at 5 hearts and 5 armor bars and also experience caps at level 15

VERY DANGEROUS CHANGES

Cats, dogs and foxes are naturally hostile to players (sense they are hostile to you they have double health and damage too)

Ghast fireballs are 3 times stronger

Ghasts shoot 3 times as fast and move twice as fast

End crystals are 5 times stronger

Blue wither skulls spawn fire and the explosion is 3 times stronger

normal wither skulls blow up 3 times stronger

the wither has 800 health and is a bit faster

skeletons and strays spam arrows

ender pearls spawn 3 endermites every time teleport

creepers are 3 times faster and their explosion is 3 times stronger

the ender dragon has 600 health

evokers spawn 3-30 vexes 

dolphins do 1 million damage 

iron golems are 5 times faster and do double damage

villagers naturally avoid players

all mobs no longer burn in daylight

you can no longer punch mobs

axolotls attack you if you are in water