The Corrupted Essence appears a large, three-eyed and winged being in the likeness of Plague Knight. It rides on top of a metal orb resembling a cauldron.
The Corrupted Essence is the second form of the Ultimate Potion after the Plague of Shadows, and the incarnation of Plague Knight's Essence overpowered and out of control. Once defeated, the Ultimate Potion finally stabilizes and Plague Knight regains his senses.
The Corrupted Essence can be damaged by hitting the flashing spot inside its mouth. It opens its mouth to attack Plague Knight or after attacking the device it is standing on is damaged after being exposed by attacks.
It can attack by:
- Shooting projectiles.
- Tackling Plague Knight.
- Bouncing, trying to smash Plague Knight.
- Creating a lot of explosive sprites shaped like Mona and with an exploding radius similar to the Big Boom.
- Although not clearly stated, this battle takes place in Plague Knight's mind. It can be interpreted as Plague Knight fighting against his wish for more power.