Okay, hes last on boss battles, and the final boss. but I'm surprised no one posted a walkthrough.
When orbs surround him, back away. they will circle him and inflict damage.
when he turns into a fish, duck. it can send you flying.
While he's teleporting, if he leaves behind a cloud, wait. it can temporarily stun you.
If he moves to a side and reaches him, look out. he lets out a bunch of projectiles, followed by a large fireball.
when he appears in the middle and grows wings, stay grounded and dodge the rings. being hit by them means instant death.
When he points his hand and three pluses appear, get away from them. they explode.
if he creates a boomerang, jump over it, then jump again.
when he grows to a huge size, stay on the edge of the screen. two lasers come out of his eyes.
if he transforms to two brackets, dodge it or jump. it also means instant death death.
if he forms a whip, jump of dodge it. It covers the whole screen.
if he appears next to you, on ground, dodge an attack sorta like triforce slash.
He also might bring out a crow gun. stay on the ground, then when it's about to fire, dodge.