Need help to beat The Cubicle on Hard

[Ťřêŵ]

I understand that he heals only when he has capsule leftovers next to it, but I only have so much space to drop unwanted capsules away from it so that it doesn't heal. Furthermore, the damage from capsules and the Sword of Flames barely makes any dent on him and his recovery rate is sky high. Are pills any good against it? Is there a better strategy that I'm missing? I'm stuck as hell...

[Ťřêŵ]

Turns out the Sword of Cruelty is better, since it deals the same damage with half the cooldown.