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Multicolored (also "multicolor", "multi-colored", "multi-color"; as opposed to "monocolored", "mono-colored" "single-colored") cards were introduced in the Legends set, and use a gold frame to distinguish them from monocolored cards. For this reason, they can be referred to as "gold" cards. These cards require mana from two or more different colors to be played. Multicolored cards tend to combine the philosophy and mechanics of all the colors used in the spell's cost; examples of such cards are Quicksilver Dagger and Niv-Mizzet, the Firemind, which combine blue's ability to draw cards with red's ability to deal (direct) damage ("pinging").
More recently, two-color "hybrid" cards that can be paid with either of the card's colors (as opposed to both) were introduced in the Ravnica set, and is considered to be of both colors (202.2d). Hybrid revolve around the mechanics and philosophies that the two colors have in common. The cards are distinguished by a gradient frame with those two colors. Multicolored cards tend to be proportionally more powerful compared to single-color or even hybrid cards, because of the restriction of having to play all the colors in the casting cost.
White-Blue is slow and steady. Typical white-blue decks stall the game and let the users cast their major spells in late game.
Ravnica guild: Azorius Senate
White-Black is about gradually killing one's enemies, with white slowing the game down and black destroying opponent's creatures and drain their lives.
Common mechanics: Lifelink, parasitism, return creatures from graveyard, massive removal, permanent exiling
Ravnica guild: Orzhov Syndicate
Blue-black is related to secrets and forbidden knowledge. Blue's emphasis of information and black's solitary nature combine to create a very secretive color pair. The opponents' of Blue-Black decks often realize that they are going to lose when it is too late.
Common mechanics: Milling, card draw, discard, library manipulation, casting from graveyard, large creatures with big drawbacks, unblockability
Ravnica guild: House Dimir
After combining Blue's desire for progress and red's impulsiveness, Blue-Red is a color pair that focus on innovation.
Common mechanics: Power/toughness switching, reusing instants/sorceries, time manipulation (e.g. taking additional turns), copying spells and abilities, changing targets of other spells and abilities, gaining control of permanents
Ravnica Guild: Izzet League
Black's anti-sociality and Red's hedonism combine to create a very sadistic and sociopathic color pair. Black-red decks typically prefer overwhelming opponents at all cost, often at the expense of their own creatures and even their users' life total.
Ravnica Guild: Cult of Rakdos
Black-Green embodies the cycle of life and death and thrives on exploiting the cycle. Black-Green capitalize on creatures that slowly grow over time or those that have special effects when they die.
Ravnica Guild: Golgari Swarm
Red-Green is very unthinking, considering the fact that it has red's impulsiveness and green's preference for instinct over mind. Red-Green decks are typically highly aggressive and attempt to overwhelm their opponents with pure strength.
Common mechanics: Trample, Land Removal
Ravnica Guild: Gruul Clans
Red-White represents enforcement of justice, as a mixture of red's readiness to take action and white's insistence in righteousness.
Common creature types: Giants
Ravnica Guild: Boros Legion
Green-White detests black's individualistic attitude and is the color pair of group and unity. Green-White thrives in being in groups.
Ravnica Guild: Selesnya Conclave
Green-Blue is the color pair of progress. Both green and blue enjoy seeing the world evolve, although the former prefers reaching it by natural selection while the latter prefers artificial means.
Ravnica Guild: Simic Combine