Sky Whale

the ground and sea have been massively expanded in terms of content. but what about the hundreds of empty blocks above us? the top of the world is often a lonely place, but it doesn't have to be.

i can see this rare mob being large, about two long by one wide ravagers worth, travelling solo or with one baby. they can only be found from y200 and up, skimming the tallest mountains, though they can be leashed and safely kept anywhere. because they float and passively grant the slowfall effect when close, crossing biomes is easy, though their size makes small spaces and portals a challenge. when leashed, their light weight means they move at player speed.

if attacked by anything such as the player or a skeleton arrow, they should hit about as hard as a ravager and have similar health. their only natural prey is the phantom. similar to the endermen despising the endermite, sky whales despise the phantom. the membranes can heal and breed the whales.

players can attach up to eight phantom membranes (each membrane adding more range) to a lightning rod to create the non-conductive 'phantom lure', that causes all nearby sky whales to guard the surrounding blocks. when any hostile mobs are within range of the rod, they attack. 

the sky whale drops normal mob exp and bones. they come in a variety of light blues, greys and white - except the black whale, which is as rare as the blue axolotl. whales must be named to be permanently kept or they will despawn with enough distance.