A and D/left and right arrow keys to move, W/up to jump, and space to throw bombs. Press space to continue/end dialog. Don't touch lasers, explosions, or Circlo. Touch green bombs to pick them up. Throw bombs at Circlo to damage him. If you beat Circlo without taking damage, post it in the comments.
Thanks to @GoldenCart for Boss Battle - Oppostomp EX - Extra Boss 1.
