DOUBLE CLICK FLAG This is a draft featuring about 85% of my latest project (12 phases). Arrow keys to move, A and D to aim your bullets (green bullets automatically target enemy), hold S to slow down. For practice, you can use the space key to set the boss's health to 1, thus triggering the next phase. Press 8 to set your health to 128 (only works in first 2 seconds of the game) The black dot in the middle of the green square is your hitbox. If that touches a bullet, you lose 1 hp and gain some invincibility frames (~2 sec, 5 blinks). You start with 8 hp, and if you reach 0 hp, you lose.
my profile is littered with bullet hells, credit to other bullet hells like touhou/undertale/jsab/etc. 7/13/20 change: reworked phase 7: bullets are 60% slower (5->2), but spawn at the same rate, so there are 150% more bullets onscreen (big number->bigger number).