In my opinion, CCG is gimmicky, but still fun; there are actually a few ways to build deck, and you can switch them for specific rooms (i.e. enemies).
There are multiple win conditions: discard opponent's cards, drain it's mana, keep you hand full so that "add junk to hand" misses you... Strategies that work vs some enemies will utterly fail vs others, right until the point there you can break the game back.
I have read that some use Tarot, while I never generated any.
Decks I used, in order that I could assemble them:
- aggro rush with junk
- Big hits relying on luck and stalling with Hearts, best cards: discard for 5dmg and "add 3 cards to deck, 1 of which deals 8dmg for 1 mana".
- Burn with "3 dmg each turn" card, as alternative win condition vs non-discarding enemies.
- Discard control, same deck as before but I stall by removing cards.
- Mana control, I fill their with junk and drain their mana
- Combo-rush with "1: draw 3, gain 9 mana and 10-mana curse" and "discard card to deal it's mana as dmg", using graveyard-tutors, deck tutors and discard synergies
This is not a trivial amount of variety.
Also, for those who are suffering: you can avoid picking temporary cards, there comes a point then Defences and Foxes just don't work with your gameplan. Gold rewards are safe to pick 100% of the time, while white should be avoided.