Rapid Fire was enabled for this.
This fight is very weird in the prototype. He's not invulnerable to normal damage, but can still be stunned by Nightmare Holes, and he can move without any pauses several times in a row.
Along with this, there's a lot of oversights, like the invisible ground after the door not being removed post-entrance and you being able to fall even after defeating him. The fight is far more polished in the final game.
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