"one more step and-"
*Step*
"FINE"
*A book and a weapon glowing with golden light appear in his hands*
"You underestimate my power. If you really think you can defeat the person who MADE THIS WORLD you have a world of pain coming."
The fight begins similarly to the Collector bossfight, but very quickly it starts using mechanics from other bosses such as trollface's clones and inkstone damage, that on top of the fact that you can't heal makes this boss seemingly impossible.
However, if you defeat me, you get the ability, to enter at any checkpoint, with any item, in any route
You could start the game with endgame gear, skip to the Collector with beginner weapons, or anything in between
And... You unlock the developer gear. Infinite attack, defense, and health
However the attack only deals enough damage to bring the boss to it's next phase, meaning it is very useful for demonstrating the abilities of a boss or searching for rare dialogue
You cannot fight me again after this, if you go through the credits again, I appear and send you to the title screen by force. No dialogue.