Use the W,A,S,D keys or the arrow keys to move. Dodge the attacks! It will take some time to get the hang of the game's moveset. There are different indicators for every attack the boss does. You might have to click the flag twice to have the game work. Trial and error is key to defeating the boss. Comment your fastest time! Mine is 35 seconds.
Heavily based on Galaxy Attack: Alien Shooter Boss and player sprite is borrowed from Galaxy Attack Everything else was me :D