In Magic: The Gathering, Power Nine is a set of nine cards that were only printed early in the game's history, consisting of Black Lotus, Ancestral Recall, Time Walk, Mox Pearl, Mox Sapphire, Mox Jet, Mox Ruby, Mox Emerald, and Timetwister.
The Power Nine are considered to be among the most powerful cards in the game. All nine cards were of the rarest level of rarity and printed only in the Alpha, Beta, and Unlimited sets, meaning they were only printed from late 1993 to early 1994. Currently, all of the Power Nine cards are restricted in the Vintage tournament format and banned in Legacy, the only tournament formats where they would be legal otherwise, and all except for Timetwister are banned in the casual Commander format.
The "Black Lotus" card can be played at zero cost, and grants three mana (the game's primary resource) when sacrificed (discarded from play). Thus, the card gives the player an enormous jump in the early stages of a Magic game. Former Pro player and Magic writer Zvi Mowshowitz has declared Black Lotus as the best card of its type of all time, claiming every deck in the history of the game is better with a Black Lotus in it. It has since been banned from all official tournament styles save for Vintage, but even there, it is limited to one copy per deck, compared to the normal allowance of four. The illustration on Black Lotus was painted by Christopher Rush, who was at the time a Wizards of the Coast employee. The Black Lotus illustration is a depiction of a black lotus flower over a foliage backdrop.
Black Lotus card is usually considered to be the most valuable non-promotional Magic card ever printed. Its Alpha and Beta versions in particular are considered to be extremely valuable, due to the more limited print runs and black borders of those sets. Alpha is the most sought after with an estimated 1100 ever printed, and beta with 3300 ever printed. A Gem Mint Alpha version of the Black Lotus was auctioned for more than $27,000 in November 2013.
The five original Mox cards are Mox Pearl, Mox Sapphire, Mox Jet, Mox Ruby, and Mox Emerald. They are colloquially known as "Moxen". They are similar to the five Basic Lands (the cards that provide the primary resource to play most cards) in that they cost nothing to play and can add one mana of a specific color to their owner's resource pool. Unlike lands, however, more than one can be played per turn. Like Black Lotus, this can lead to extremely powerful plays much earlier than normal. All five Mox cards were illustrated by Dan Frazier. In each artwork, a different piece of jewelry is depicted.
Ancestral Recall allows the player to draw three cards at an extremely low cost. It originated as part of a set of five cards known as "Boons", one of each color, which gave three of something (e.g. mana, life, damage) for the cost of one mana. Ancestral Recall is the only rare Boon and the only one not to have been reprinted since the Unlimited set.
For a very low cost, Time Walk allows a player to take an extra turn. In a game that involves a constant build-up of resources over time, a full turn's additional development turned out to be far more powerful than Magic's early designers had imagined. Several cards that grant additional turns have been printed since Time Walk, but always at a much greater cost.
In Time Walk's early development version, it originally had the text "Target player loses next turn." Richard Garfield tells an anecdote about a playtester telling him that he had a card in his deck that would guarantee he would win the game on the next turn. Garfield could not figure out which card this could be, until the playtester showed him a Time Walk, and pointed out the alternate meaning of the word "loses". The wording was changed prior to the release of the game.
While the other Power Nine cards are simple in concept, Timetwister is more complex. It forces each player to shuffle their hand, graveyard, and library together and then draw a new hand of seven cards. Because it affects all players, it may not be apparent at first why Timetwister is a powerful card. Its power lies mostly in situations where the player playing it has fewer cards in his or her hand than the opponent, and has established a powerful board position—Timetwister does not affect cards already on the table. The player casting Timetwister can essentially catch up on cards in hand, and potentially get back powerful cards that were discarded, without giving up a dominant board position. Unlike the other cards in the Power Nine, Timetwister therefore requires a deck to be more carefully built in order to exploit its power.
In the past, the Power Nine have only been available on Magic Online as a part of Cube Drafts, which cards are not allowed to be kept by players after the game. But there has been no way to permanently own any of the Power Nine cards on Magic Online, and Vintage format was not sanctioned at that time either (although there was an alternative format named "Classic").
In June 2014, WotC officially supported Vintage as one of the sanctioned format in Magic Online, and Vintage Masters, a booster specifically providing essential parts in Vintage format, including all Power Nine cards, was released in a limited period.  They will appear only in the premium foil slot where they could be either foil or non-foil as a special rarity. On average it will take 53 packs of Vintage Masters to pull one of the Power Nine. 
The implementation of the Power Nine cards online are functionally identical to the original cards, but have oracle text, different artwork and are displayed with a modern card frame. With exception of the Black Lotus, the illustrations are those that were originally given to the winners of the Vintage Championships as alternate Power Nine artworks. The Black Lotus received a new artwork by Chris Rahn.
The Blacker Lotus was a satirical card in the parody Unglued set which produced four mana, although it required the user to physically tear the card up after use. Jack-in-the-Mox from the same set works like a regular Mox but produces either a random color of mana, or destroys itself, depending on a die roll. Mox Lotus, from the later Unhinged parody set, provides infinite mana of any color and immunity to mana-burn (now redundant due to rules changes), but costs fifteen mana to play.
The Power Nine are among the very few widely-recognized cards never to have received updated artwork from their original printing. As a way to rectify this, since 2003, the winner of the annual Vintage Championship has received a unique, oversized Power Nine card featuring brand-new art. These prize cards are considerably larger than actual cards, and therefore cannot be used in play. The five Mox cards feature artwork that represent the settings of the Magic expansions released in their corresponding years. Their artist, Volkan Baga, has also illustrated two other Mox cards—Mox Opal and the reissued Mox Diamond—in the same style. The following cards have been given to the winners:
- 2003: Black Lotus to Carl Winter (Artwork by Christopher Rush)
- 2004: Timetwister to Mark Biller (Artwork by Mark Tedin)
- 2005: Ancestral Recall to Roland Chang (Artwork by Mark Poole)
- 2006: Mox Pearl to Travis Spero (Artwork by Volkan Baga)
- 2007: Mox Jet to Stephen Menendian (Artwork by Volkan Baga)
- 2008: Mox Ruby to Paul Mastriano (Artwork by Volkan Baga)
- 2009: Mox Emerald to Itou Hiromichi (Artwork by Volkan Baga)
- 2010: Mox Sapphire to Owen Turtenwald (Artwork by Volkan Baga)
- 2011: Time Walk to Mark Hornung (Artwork by Chris Rahn)
- 2012: Timetwister to Marc Lanigra (Artwork by Matt Stewart)
- 2013: Ancestral Recall to Joel Lim (Artwork by Ryan Pancoast)
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- "The Power Nine"—Images of all Power Nine cards
- The Gatherer Card Database—This database has detailed information on all other cards mentioned in this article