Spoiler Alert! As of right now all of the large flying bosses are very easy to kill with a simple terrain exploit. Build yourself a little shield of cobblestone with one brick missing and shoot arrows at the boss. It takes a couple minutes but there is no way you will die. Over all there are lots of things I would like to see to make bosses more fun and challenging but this simple suggestion of mine will go a long way to help that. Suggestion: All of the bosses should have the ability to clear out large chunks of terrain. Not only would this be very fun during a fight to have for instance to have the jelly boss throw out explosive goo that explodes terrain but it would also stop this exploit. Its a win/win in my opinion.
How about fighting bosses in generated arenas that you can't destroy or build in, and you can only spawn bosses in the arena. That way nobody could cheat.
I would suggest that bosses and rare monsters should be able to break past blocks. They should either have an ability that breaks blocks around them or be able to pass through blocks (like that worm boss in terraria). It is just stupid being able to lock in every single hard mob, it makes the game way less challenging. Also, this way (making rare monsters harder) they could increase the return from killing one.
