The game gives you a special goal in each zone you enter (like find a certain item or kill special mini-boss enemies) and some rooms have challenge crystals which typically give you a wave of enemies to
defeat although sometimes they have other goals (like don't take
very much
damage) which helps to keep things interesting.
Whenever you want, you can hit him, and he'll use up some of his magic power to
damage or
defeat every enemy on the screen via a variety of
very powerful spells.