What is Modified Format?
The Modified format is the standard tournament format for Premier Pokémon events. This format will be used at all premier events unless specified otherwise. The Modified format for the 2013–2014 tournament season contains the following:
In addition, new sets will become legal 3 weeks after their release, per the Play Pokémon Tournament Rules. With the exception of basic Energy cards and previously printed cards that appear in Modified legal sets, players may not use cards from older Pokémon sets prior to announced sets. Players using previously printed cards that appear in current Modified format legal sets must play those cards using the wording of the most recent printing of the card. (some reprints require reference cards)