Urza's Saga is the fifteenth expert level set in Magic the Gathering. It was a set comprsed of 350 cards. It is known for being one of the more powerful expansions in the history of Magic the Gathering. The set introdusced mechanics such as free spells, echo, cycling, sleeping enchantments and growing enchantments.
Notable cards in the expansion were Tolarian Academy, Gaea's Cradle, Yawgmoth's Will, Morphling, Lightning Dragon, Sneak Attack, Rewind and Fluctuator. This set was one of my favorite expansions of all time. It was very powerful even by today's standards. In fact several cards were restricted at the time. The set was also very fun to play with because its mechanics allowed for more deck possibilities and better card efficiency.