Simply beat the first level. Nothing else to it.
Difficulty does not matter
I wouldn't worry about the two small satellites he launches out. Just worry about the main color and the few small bullets are easy to avoid.
He will start white, then fire black, and then back to white.
If you're really crafty, you can stay the opposite color the whole fight and just dodge the spray. Or, if playing coop, one player can match his fire color, and the other can hide behind him as the opposite color, so all the bullets are absorbed by the front player