Board Thread:Fun and Games/@comment-24768103-20141108000930/@comment-17259909-20150114221338

19 & 20. Nope.

OPN21. No.

The correct answer was Ogyu. He's a video game-only character and a Card Hunter in Greed Island. I found evidence that he and Killua interacted here, but I have no evidence that he met Gon.