Wizards of the Coast only printed enough Legends cards to fill pre-orders that were placed by a certain date. As a result, this is one of the most popular Magic expansions ever.

Legends isn't only popular because of the small number of cards printed. Legends introduced players to legendary cards (cards that there can only be one of in play at a time) and multi-colored cards. Both of these themes became very popular with players and have been used in many sets since then.

Legends also introduced two new game mechanics: Rampage and Bands With Other. Neither of these mechanics were very popular among players, but they were a good attempt nonetheless.

Notable Cards:
Mirror Universe Buy and Underworld Dreams Buy were immediately recognized by players as very powerful cards. They allowed for such powerful combos and unstoppable game-wins, that they were quickly put on the DCI's restricted list.