Bedrock 2.0 Add-on for Minecraft PE adds 18 new mobs, bosses, new ocean life and even new ores and stones ( they will change texture ). If you want make your world different I recommend this addon as well. You can also have a big challenge to battle with 2 bosses.
Which new mobs you will see?
New villagers: village warrior, Cannon-man, sniper and Archer villager and turreteer
Hostile mobs: Stone eater, Ender carcass, Frost eater, Ryft, Skeleton knight, Sunken
Bosses: Chill rave boss, Wraithen boss
Mobs which live under water: Lion fish, Mahi mahi, Lion’s mane jellyfish, Jelly fish
Inanimate entities: Turret, Cave crystals
some screenshots are below
Download this addon for Minecraft PE 1.8/1.11 +