@ Matchbox:It's not tournament legal because it's too old. Only certain cards are currently legal to be played in a tournament. You can find the list of tournament legal cards @ http://www.go-pokemon.com/op/tournaments/card-dex.html
It's likely that at the next rotation Diamond and Pearl base set, Mysterious Treasures, Great Encounters and Secret Wonders will no longer be tournament legal.
Some events still let you play with cards from any set, and if your only playing casually you can use what you like! ^^
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