Bosses should be able to break terrain blocks with their shots. They should target newly placed blocks. This is to make it harder to cheese the bosses and make the game harder to progress. Also bosses should be able to bash blocks so when they are blocked in then they can free themselves. Blocks hit by boss' head should be destroyed instantly
Double that. But to add some variety, bosses with less than 50% health can just run away really fast if they're unable to reach player for 7-10 secs. Since the player is more interested in defeating boss, he will play more fairly to keep his attention.
