A Rare 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, every player must have exactly 40 cards in their
Main Deck. The Main Deck must include cards of the following rarities:
If a player sides in cards from their
Side Deck between Duels of a Match, the rarity composition of the Main Deck must still exactly follow these rules after using the Side Deck. There are no special rules for the Extra Deck.
A Rare Format was the official
Pegasus League format from June 1 to August 31, 2010, using the  March 2010 Advanced Format Forbidden and Limited lists.
"WELCOME TO THE PEGASUS CHALLENGE!". Konami . http://www.yugioh-card.com/en/league/pegasus_league/index.html . Retrieved July 27, 2015. ↑
"BIENVENIDO A LA LIGA PEGASUS!". Konami. Archived from the original on September 29, 2010 . http://web.archive.org/web/20100929110329/http://www.yugioh-card.com/lat-am/league/pegasus_league/index.html . Retrieved July 27, 2015.