Minecraft needs new boss

Depends. I've seen some creative bosses made from command blocks, so I don't think the game necessarily "needs" bosses when people can already create and share their own. Especially if you download a world somebody else made and play through it, you can find a lot of creativity in the creator's work.

But when you're talking about Survival mode, then it's a little different. Personally, I never felt the need to fight any bosses in Survival mode, but I think it could add more elements of gameplay under the right conditions... just that it's not really needed, but would be a nice addition.

 

I want more powerful but tameable bosses. It can ride or fly for example. Can be killed with long-term missions and weapons instead of killing in a single shot.

 

I feel like there are already mobs (particularly bosses) that can fly (like The Wither and the Ender Dragon). I think one idea of a boss would be one that could always just lunge at you and outpace you, so if you try to run away, you'll have a hard time running away. This would encourage you to use your shield more often and figure out a creative way to block yourself from the boss from time to time. I think there are opportunities for new ideas, but I don't really know what it would be like when actually implemented.