Jaiz Mobs adds 20+ new features (as of the full release - 0.11.1.20.4 and up) This mod aims to improve the diversity of mobs and add functionality to the world in areas it may have been neglected.
there's 4 types!
Ridable underwater mount
dripstone hostile mob
he spawns in stony shores
there's also 4 other mobs there
first mobs added
there's a small version too!