I disagree, it's not a sideways strolling platform game, it's like those that want this animal, or that animal - is this Minecraft or Petcraft?

A big bad bird found in Jungles called Roc. I'm planning on making this in a project I'm working on.

I agree with Hashs, Nether boss that isn't just "the wither," which you don't need to spawn in the Nether so doesn't explicitly count... maybe some sort of Ghast-like boss, something that flies or takes you near the lava to make you take a risk.
Also, in the theme of "We need a cave update!", a cave boss, maybe in some form of dungeon. Golem, maybe? Food for thought.

Herobrine?

how about dwayne the rock johnson

If you want more bosses, my datapack Undermagic adds 2 additional bosses to the game along with new armor sets and weapons to fight them with. It also adds a higher difficulty level that gives all 4 bosses new drops and makes them considerably harder.

Shameless plugs aside, a real nether boss would be nice (the Wither doesn't count). Also, dragons other than the Ender Dragon would be interesting. These two could possibly go hand in hand, such as a lava dragon sort of thing, if that makes sense.

I want a boss in the Jungle temple, that is like a mummy or something.