Uncommon is one of the three rarities in Fight Klub.
Uncommon cards you may use up to 3 of in a deck. They come packaged 1 each in a kilo.
Uncommon cards have a U in the lower right corner between the set number and the card number.
Therefore a card from set X that is number Y would have X-U-Y in the lower right.
example: Puzzle Piece is card number 86 from set 1 so has 1-U-86 printed in the lower right corner.