The steps required to perform the glitch:

• Enter the boss stage.
• Do not move and wait for the boss to attack.
• Without moving jump up and attack the boss after it moves down.
• Wait for the boss to move down a second time.
• Attack the boss once more and it will enter the glitched state.
• Use Down+B to attack the boss faster. Do not hold Down while doing this. You must press Down+B then release both buttons then press them again between attacks.