well, the cards are used to daily questes.
daily quests: go get this item and get something in return
1st quest gives you some useless potions that makes u look like a animal.
2nd quest give you 2 loot potions, one of them increasing the tier of the drops you get. and the other to increase the drop chance.
A potion that boosts the tier level of dropped loot. Up to +3 tiers! Lasts 30 minutes.
A potion that causes enemies to drop more loot at a rate of 1.5x normal! Lasts 30 minutes.
3rd quest gives you a skin, but mostly the slime qizard skin.
when he is open, theres another quest of which u need to get all the cards, and he will reward you with a token. you can use the token to get a free item, from the orbs outside his "shop". how you do im not sure of. altho there will spawn 3 items in the smaller orbs and you will have to pick one of them, you have 10 seconds to pick.
hope this help'd you