I've played the older versions, and really, you can't.
Extremeness is summoned by someone who is "Very extreme" which you get when you win the game.
The creator made it look like you could get him, but you needed to meet a certain requirement, which was winning, and after that, Extremeness comes out of the altar, making it look like you summoned him.
It's all an illusion (can't think of a better word.)