Caste Party Format is a Deck format used in some Pegasus Challenge tournaments. It can be run in either Advanced Format or Traditional Format. In this format, all cards in the player's Main, Side and Extra Deck must be of the same rarity, which one being the Deck builder's choice. Cards with the same name but different rarity cannot be substituted. Caste Party Format was the official Pegasus League format from October 1 to 31, 2009, using the September 2009 Traditional Format Limited lists.