Flipping a coin is method of randomization of effects with two possible outcomes of equal likelihood.
The coin flip was introduced as a mechanic in Arabian Nights with Mijae Djinn, Ydwen Efreet and Bottle of Suleiman. Any color can flip coins, but red does it most. It also appears on artifacts. If the card is multicolored, so far it always has been red/blue. There is one blue card with the mechanic (Zndrsplt. Eye of Wisdom), one black card (Tavern Swindler) and one green Un-card (Flock of Rabid Sheep).
From the Comprehensive Rules (Guilds of Ravnica (October 5, 2018))
- 705. Flipping a Coin
- 705.1. An effect that instructs a player to flip a coin may care whether that player wins or loses the flip. To flip a coin for such an effect, the player flips the coin and calls “heads” or “tails.” If the call matches the result, the player wins the flip. Otherwise, the player loses the flip. Only the player who flips the coin wins or loses the flip; no other players are involved.
- 705.2. If an effect instructs a player to flip a coin and that effect cares only whether the coin comes up heads or tails without specifying a winner or loser of the flip, that player flips a coin without making a call. No player wins or loses this kind of flip.
- 705.3. A coin used in a flip must be a two-sided object with easily distinguished sides and equal likelihood that either side lands face up. If the coin that’s being flipped doesn’t have an obvious “heads” or “tails,” designate one side to be “heads,” and the other side to be “tails.” Other methods of randomization may be substituted for flipping a coin as long as there are two possible outcomes of equal likelihood and all players agree to the substitution. For example, the player may roll an even-sided die and call “odds” or “evens,” or roll an even-sided die and designate that “odds” means “heads” and “evens” means “tails.”
From the glossary of the Comprehensive Rules (Guilds of Ravnica (October 5, 2018))
- Flipping a Coin
- A method of randomization with two possible outcomes of equal likelihood. See rule 705, “Flipping a Coin.”