SOLVED. Four kids playing a fantasy card game in small town [s]

[Bryan]

The book's protagonist is a young male, probably in his teens, and he plays a card game with three of his friends. He buys his cards at a small shop and I think they play the game in the back of the shop sometimes.
In the beginning they find that a bully from their school bought some cards too. They have a secret house or tree house in the forest and they get in with a secret knock that I believe has four knocks, one for each of them.

That's about all I remember.

[Tab]

How many years ago did you read this book? Anything about the cover?

[Bryan]

Tab wrote: "How many years ago did you read this book? Anything about the cover?"

I read it about five years ago and I can't really remember anything about the cover.

[Tab]

The Revenge of the Shadow King ?

[Piper]

To me this sound like Yugioh which is a series based around card games and e is bullied by one kid who also has card called Kaiba. He has big hair which is blonde black and red hope this helps.

[Bryan]

Tab wrote: "The Revenge of the Shadow King?"

Yes, That's it! Thank you.