I finally beat them, with the winning deck as follows:

• x1 Potato
  
• x1 Metonym - safest to play as a last hit to get Cardplaya to 0
  
• x2 Jenny Fox
  
• x1 Ittle Dew
  
• x3 Heart
  
• x1 Goddess of Explosions
  
• x2 Goddess Buster
  
• x2 Fire Mace
  
• x1 Dumped X
  
• x1 Evil Easel
  
• x2 Cyber Skull
  
• x1 Boss Trio
  
• x1 Bees X
  
• x1 Bees
  
• x2 Benny
  
• x2 Fasen

The idea is to block cardplaya as much as possible and still do damage.

Generally you want to do quick damage - and better yet not actually spend a turn on doing the damage. This is why we use cards that damage on placement, where the card may be sacrificed blocking one of cardplaya's cards.

Potato (and thereby also Fasen) additionally helps with fast damage, by doing damage on draw - and Fasen may also provide some card activation, as it is one of the few cards in the deck with more than 1 turn to resolve.

The Heart cards are a bit of a joker, as you may be unlucky to pull them all on full health, but they may still come in handy for card activation.

The Goddess of Explosions and Goddess Buster cards are kind of the trumph cards. I used them as soon as i had all 3 on my hand, and then put them down in places where they wouldnt activate AND would block cardplaya's cards, as the special ability of playing Goddess of Explosions last will result in lots of damage - and get rid of shield if they have it.

Boss Trio should be played as soon as possible and if possible as far left/furthest up on the board as possible (because of the way the cards are resolved) - but bear in mind not to block too many of your own arrows.

Bees and Bees X are super useful to render Cardplayas cards useless, but you may want to be careful with activating them if your own hand is full of useful cards (it would suck to lose the goddess of explosions combo because the card was silenced, where on the other hand on-draw cards may be a good choice to play)

Lastly, Dumped and Evil Easel are really only used to prevent powerful cards like the legendary "shield on card played"-card

A sidenote: I really didnt want to grind for cards, so these were all in my inventory, but as you get them by random chance it may not be possible to complete the deck, if that's the case you may want to use other cards with 1-turn damage/health (i.e. Jenny Flower) or jokers (i.e. Slug, Jelly), and i would advice against shield cards (besides maybe Chilly Roger).

The deck and deck description was originally posted in the discussions, specifically:
How to get the last two achievements?

Originally posted by sfnhltb:

Probably not the best, but the deck I was able to win without too many problems (2/0 first time I used it, but after trying a few different deck themes) was:

CardPlaya x 2
Rainbow Ring
Prince Hingst x 2
That Guy x 2
Metonym
Lemon x 2
Dark Lord X
Alpha Strike
Dumped x 2
Queen Amelia X
Jenny Bunny X
Jenny Bunny x 2
Razzle Dazzle x 2
Boss Trio x2
Cyber Jenny
Nils

Essentially you use the control stuff (switch, remove, silence) to grab or stop those nasty draw damage/heal cards from doing much, then use Lemon or CardPlaya to give Hingst/Metonym/That Guy, or CardPlaya/Dark Lord X to steal the draw activated cards and give them back some of their own medicine. I put Boss Trio in due to often being behind in health early as you are concentrating on knocking out enemy cards rather than damage, it can be a good way to catch up once things are in hand.

The main weak point of their deck is that about half of it is snakes + wands + wand generators to keep those cards alive longer - if you kill or steal those key cards before they do much damage it makes the deck toothless, but that requires a lot of control cards, so then you need to be able to do enough damage with a relatively limited amount of cards left. Another possibility would be to mill things out - add tosca, blueprint, Itan's shop, horsegun, maybe some heals and shields and win via fatigue, although this might dilute your control cards too much later on.

The deck description was originally posted in discussions, specifically:
Where is the legendary card player?

Originally posted by lionhart:

After struggling with this for quite some time, I finally found a deck that can reliably beat the legendary card player.

Use the text filter to search your deck for the word "placement", then select cards that have any of the following effects upon placement:

- Heal
- Gain shield
- Deal damage
- Add cards to your deck

The strategy is to try and block the opponent from linking and activating their cards. Don't try to form your own chains at all, just place your cards where they will block the opponent's arrows. In fact, you should try to avoid forming your own chains. The goal is to gridlock the entire board; every time the board resets the opponent will take damage, and they will also begin taking fatigue damage when they run out of cards. Just wait it out; the fact that you are healing and shielding with every other card placement should keep you alive long enough to win.

I haven't tested it yet but I am pretty sure that this deck/strategy could defeat any other opponent in the game as well.

Other recommended card effects are:

Originally posted by kazekind:

nice strategy. i used activating cards (like key x), removal cards, and cards that would tick hers down quicker, along with some self healing. I didn't try locking down the board much but your way sounds maybe easier than mine.

Or from the original poster

Originally posted by nashix:

her card is cheaty, so "switch-color" cards are useful.
I used Jenny Bunny X and Card Playa:)

If you have any other deck recommendations, feel free to put them in the comments! :-)
Any feedback on the decks posted here - or with your own - will also be greatly appriciated.

Gods peed, Cardplaya!