BOSS

what's the best way to create bosses in the game?

I think of defense-and-attack bosses

they are on top for example shooting and attacking and then go into a paused state to take damage from the player.

A mix of conditions and enemy state. You can set an enemy state with a variable and based on this decide what action it will perform. Then you change this state based on factors, whether it chooses random actions or it does something when attacked etc.