Ultimate Evil

Pure Evil3.

The evil that bests (or worsts?) all other forms of evil by being every evil at the same time but intensified. If the Villain is this, then they can be practically unstoppable until they meet up with the Hero who may be the only one with the power to defeat this evil.

Having something be The Ultimate Evil (or anything else considered "ultimate") might be a desperate move by the creators to come up with something more extreme than anything any other creators can come up with.