Historical Rules · 13 July 2018
Rule 705.1
Official source text from the 13 July 2018 Rules release
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.