Card advantage is a word for a deck or player getting the best use from those resources. There are multiple resources in Magic, but the most basic and universal of those resources are cards, which obviously every deck contains.
Defining card advantage
In basic terms, each card that is drawn allows the player to get closer to however they intend to win the game, and the same is true for the opponent. Having and gaining card advantage over your opponent means that you are closer to having the right cards to win the game than they are. Card advantage is an incremental advantage and is mainly associated with control decks, who seek to gain card advantage over time before delivering a killing blow, while it is not particularly relevant to aggressive decks that seek to win quickly while their opponent is still drawing cards and finding the right pieces.
In a normal game, each player has 60 cards with which to win the game, but they in fact have access to far fewer cards than that, because of the restriction on hand size, and only drawing one card per turn. Additionally, decks need to run in excess of 20 lands while functionally can only utilize seven to eight before running out of spells. This means that all decks will inevitably have a large number of blanks in them in the late game, and so the general approach to Magic is dichotomized as such: play to the board and kill your opponent before your resources deplete (the aggro deck), or draw more cards than your opponent to generate card advantage, and in doing so giving you access to more resources than they have (the control deck).
However, simply drawing more cards is not the only factor in card advantage, and it similarly applies to how efficiently cards are used. If everything were equal, then each card played would be canceled out by the next card played by their opponent. If this were the case, neither player would have any card advantage.
The most basic way to gain a player card advantage is to simply draw cards through spells or abilities. Some spells like Divination simply draw cards while others like Ponderallow the player to chose which card they draw. A spell which cantrips is also a way to gain card advantage, as a player can impact the board while drawing a card. Various effects can cantrip, but the more impactful it is, the more expensive they become.
Another way to gain card advantage is to use one card to counteract two of their opponents'. This can be achieved either through using inherently more powerful cards (using one Wrath Of God to kill two creatures instead of two Incinerate) or through playing in such a way as to create a "two for one" situation even with a weaker card. An example of this would be using Incinerate to kill a creature in response to your opponent casting Giant Growth on it. This kills their creature and means their Giant Growth has been wasted, leaving him with one fewer resource to use.
Another, less literal, way is for a player to either convert "dead" resources to "live" ones, or force "dead" resources on one's opponents. This is known as "virtual card advantage". Faithless Looting, on its surface, does not generate any card advantage - in fact, it reads as card disadvantage, costing itself as a card while looting two. However, it was the backbone of many powerful decks, of which the most basic function was to discard lands, which were often dead after one had enough in play. The fact that it was so cheap meant it was easy to exploit alongside various graveyard-based and spell-based synergies. On the other side, control decks often play no vulnerable creatures in their main deck. This meant that opposing decks looking to interact with creatures were often stuck with four to six additional dead resources over a game. While not guaranteed to impact a game, the control deck often stretched out the game until a point where the opposing deck's dead resources caught up to them. Prison decks do this more proactively with cards like Ensnaring Bridge: a card that, when one's hand is empty, invalidates all attackers, making them "dead" until the bridge is removed.
Each of these has its disadvantages from a gameplay standpoint. Modern Constructed Magic has increased the power level of creatures to the point where playing to the board is generally the more effective strategy. As a board of two uncontested creatures is now threatening, board sweepers have gone from immediately winning spells to mandatory pieces to not lose, and many creature decks can easily recover. Immediate two-for-ones like Ravenous Chupacabra or Bright Reprisal, for example, lose a lot of luster when the caster takes four to six damage each turn, even with the removal spell. Furthermore, fizzling your opponent's tricks with spot removal is nearly non-existent, again as tricks are no longer necessary to attack. Finally, raw card advantage follow the same problem as the previously mentioned cards: casting these spells cost turns, and each turn costs life. The fact that the draw spell may yield only lands and other draw spells is a real cost. Modern control decks use all of these in varying quantities, in order to force the attacking deck to make tough choices, which usually slow them enough to regain control.
Part of this dynamic comes from the deckbuilding costs of control decks and the nature of threats and answers. A threat will be a problem each turn it persists, while answers can only reprieve from one of them. Trying to remove each threat as it appears will work until one runs out of answers, and the last threat will win - hence, a control deck can't play the same land count as an aggro deck. Therefore, use card advantage spells; but then, this means a control deck now has higher odds of drawing lots of land and draw spells and not enough answers. This is why planewalkers are important on both sides; persistent and diverse threats for aggro decks, and turnwise, zero-mana investment advantage for control decks.
Mastering the concept
As is hopefully clear by this point, card advantage is a difficult topic to describe. However, learning the concept of what it is, and how to gain it allows you to win games that might otherwise be impossible. However there will often be a choice between simply protecting your current position, and gaining card advantage, and knowing which to pursue is one of the most challenging aspects of magic, and mastering it will make you a far better magic player. If an opponent is forced to use a card to protect their creature or spell (perhaps using Vines Of Vastwood to save their creature) then you remain equal in terms of card advantage (you lose one card, as do they) but they maintain an advantage on the battlefield. In this situation, however, other things are also happening in terms of incremental advantage. If, for example, they were not able to cast Vines with kicker, and therefore had to use it exclusively to defend his creature, then you likely do gain some advantage, because you force him to use a card that they would rather use in another much more aggressive way. If you are very low on life and have to use another removal spell to survive, you lose card advantage, but you gain another turn to draw cards and find a more permanent solution.
Card advantage is often the defining factor in control vs control matches, with the victory not going to whoever topdecked their finisher, but who best optimized their use of mana and cards, so that they had the mana to cast their win condition, and created the most opportunities to make that draw.
On the other side to card advantage from drawing cards, you can attack your opponents' hands to create card advantage by using spells that make them discard. Untargeted discard is the least desirable, as it allows them to pick which card they can manage best without, while targeted discard such as Inquisition of Kozilek can allow you the opportunity to attack either the opponent's creatures to protect the board, or their own card advantage engines, depending on the game state.
A final approach to gaining card advantage is through cards which can be used multiple times, through mechanics like Buyback on Forbid, or using cards that fill multiple roles in your deck like Snapcaster Mage, Venser, Shaper Savant or Mystic Snake
Tempo is another concept closely related to card advantage, which seeks to win not by directly killing his creatures, but by disrupting their mana curve by bouncing creatures and drawing cards. In these types of deck cards like Remand when used correctly can be a Time Walk giving you access to more mana (both by being cheaper than any other catch-all hard counter, and giving you another turn to play a land), buying time, and protecting your board position and replacing itself in your hand. While on the surface Remand is one-for-one in terms of card advantage, you gain 'half a card' in that situation, because while your opponent remains with the same cards as they had their last turn, but you gain another card from your library.
Blue is the color that is most associated with card advantage as a mechanism to win games. It contains the most cantrips, as well as the purest card draw and deck manipulation. It is certainly possible for a purely blue mage to stall out a game long enough, using continuous counter magic, bounce spells and end of turn card draw (or cards that allow all of the above like Cryptic Command) until they get a bomb Consecrated Sphinx (which doubles as a card-drawing engine) to fly in the damage they need. However, these approaches while very good at gaining card advantage are seldom the best ways to win games or protect the board state. Black provides discard and mana-efficient kill spells to disrupt the opponent's game until your countermagic gets into gear. Red offers aggressive creatures to block in the early game or apply pressure, and reach in the form of Fireballs to close a game out from nowhere. White gives some of the best spells to gain card advantage through destroying creatures in Wrath effects (which can turn into a 5 or 6 for 1), as well as a string of little dudes either with interesting effects (first strike, flying, protection) or as cheap and efficient token makers alongside Glorious Anthem effects to block or eventually to gang up and charge into the Red Zone. Finally Green offers mana acceleration to quickly move your deck from the troublesome early turns, where card advantage is much less relevant and harder to find, right up to six mana, allowing for multiple counters or draw spells in a turn, pushing card advantage from incremental to decisive, and of course, offering casting a massive green creature of stompy goodness, while leaving enough mana to counter anything that threatens it.
Card advantage comes from many different places, but in some respects, almost every decision you make in a game of Magic is made with it in mind, subconsciously or not. Learn how to gain incremental advantage and it adds up faster than you might think. Again, this article is not perfect, because no one really agrees on exactly what it consists of. But hopefully, this will give you a better understanding of what it is, how it works, and why it is so very important.
- Brian Weissman (October 12, 2009). "Forgotten Lore: Taking Card Advantage". magicthegathering.com. Wizards of the Coast.
- Ted Knutson (September 23, 2006). "Introduction to Card Advantage". magicthegathering.com. Wizards of the Coast.
- Mike Flores (February 10, 2014). "Card Advantage". magicthegathering.com. Wizards of the Coast.
- Mike Flores (March 17, 2014). "Card Advantage "Two-for-Ones"". magicthegathering.com. Wizards of the Coast.
- Mike Flores (May 5, 2014). "Card Advantage—Life and Card Advantage". magicthegathering.com. Wizards of the Coast.
- Mike Flores (June 9, 2014). "Virtual Card Advantage". magicthegathering.com. Wizards of the Coast.
- Reid Duke (August 25, 2014). "The Basics of Card Advantage". magicthegathering.com. Wizards of the Coast.
- Reid Duke (November 17, 2014). "Tempo & Card Advantage: A Delicate Balance". magicthegathering.com. Wizards of the Coast.