Neat game! Learning the bosses' patterns is nice, and the rock dude looks cool!
It's good that the majority of the attacks have an indication of when they're going to happen. I did have some trouble with the laser attack from the flame guy - it took me some time to notice that its eyes would glow red before shooting a laser.
I liked gaining new attacks, it gave me more options on how to defeat the bosses. I do feel like the player's delay between summoning the lightning strike and the lightning hitting the ground was a bit too long at times, but after a while, I could predict the bosses' movement enough to time the lightning, which was satisfying.