Himself

Sylas felt a great deal of pressure on his mind, but his stubbornness bore its own fruit. 

He had gone through cycles of different schools of thought in this world. At first, he refused to acknowledge that a metric could decide his Will. Then he was forced to accept that maybe there truly was a technology out there beyond his understanding that could do precisely that. But the more he learned, and the more he came to understand that even the system was flying blind in regard to Will a lot of times, the more he realized just maybe… he had originally been correct in his stubbornness. 

There was a reason he had used up 1010 Will during his battle with the Glass Monkey, and yet he was still standing here just fine without a single dip in his Will stats. 

But it was also because of this sacrifice that he wasn't in the best position to fight such a battle of Wills… and the Greed Seed seemed to be very much aware of that.