Figment (Miniboss)

This mob would be a phantom boss of sorts, that only spawns,

A: After you have been to the nether.

B: After refusing to sleep for 50 in game days.

It would look a bit like the ender dragon, as a foretelling to those who haven't yet fought it, and a reminder of the past for those who have. The main difference would be it would blend into the night really well. When fighting it, it would give you blindness randomly (Similar to the illusioner) and would have the ability to imitate certain mobs like a parrot to scare the player. After it is killed, it would drop 2 - 5 phantom membrane, and a new item called a Phantom Memory. It could be used to craft blindness potions.

Finally, after fighting this boss, you could be able to get an elytra enchantment that would allow you to go faster, maybe even allow you to take off anywhere to solve the... bedrock situations.