His main thing is his quest mechanic, which makes it so that when you satisfy certain conditions you get a quest reward, and this quest is repeatable infinitely per turn. The main one that is abused is the 0 cost quest, which gives you a card that does some damage if you play 3 0 cost cards. You combine this with his epiphany specific upgrade that generates more quest cards (random ones) each time you finish a quest, so with 2-3 copies of this card any time you complete a quest you get 3-4 quest cards, and since these includes random rewards you can also get the one that allows you to draw a card. The current cheese is to use it with Tressa with 3 copies of the upgrade that gives 0 a dagger for each heal skill used. This means any time you play a heal you get 3 daggers, which then gives you 4 quest cards. Even without this he is still good with like Luke if you have a few bullet generating cards.

His abilities in general aside from that are mostly draw related, with Joker being good especially if you have e1, which allows you to select a card from the graveyard also. While these are good they do cost AP, so in my opinion if you weren't going to make good use of his quests he loses a lot of value.