To double an amount of damage a source would deal, that source instead deals twice that much damage. This is a replacement effect.
April 17, 2020 · Ikoria
A spell or ability may instruct a player to exchange two numerical values. In such an exchange, each value becomes equal to the previous value of the other. If either of those values is a life total, the affected player gains or loses the amount of life necessary to equal the other value. Replacement effects may modify this gain or loss, and triggered abilities may trigger on it. A player who can’t gain life can’t be given a higher life total this way, and a player who can’t lose life can’t be given a lower life total this way (see rules 119.7–8). If either of those values is a power or toughness, a continuous effect is created setting that power or toughness to the other value (see rule 613.4b). This rule does not apply to spells and abilities that switch a creature’s power and toughness.
July 12, 2019 · Core Set 2020
A spell or ability may instruct a player to exchange two numerical values. In such an exchange, each value becomes equal to the previous value of the other. If either of those values is a life total, the affected player gains or loses the amount of life necessary to equal the other value. Replacement effects may modify this gain or loss, and triggered abilities may trigger on it. A player who can’t gain life can’t be given a higher life total this way, and a player who can’t lose life can’t be given a lower life total this way (see rules 119.7–8). If either of those values is a power or toughness, a continuous effect is created setting that power or toughness to the other value (see rule 613.3b). This rule does not apply to spells and abilities that switch a creature’s power and toughness.
May 3, 2019 · War of the Spark
A spell or ability may instruct a player to exchange two numerical values. In such an exchange, each value becomes equal to the previous value of the other. If either of those values is a life total, the affected player gains or loses the amount of life necessary to equal the other value. Replacement effects may modify this gain or loss, and triggered abilities may trigger on it. A player who can’t gain life can’t be given a higher life total this way, and a player who can’t lose life can’t be given a lower life total this way (see rules 118.7–8). If either of those values is a power or toughness, a continuous effect is created setting that power or toughness to the other value (see rule 613.3b). This rule does not apply to spells and abilities that switch a creature’s power and toughness.
January 25, 2019 · Ravnica Allegiance
A spell or ability may instruct a player to exchange two numerical values. In such an exchange, each value becomes equal to the previous value of the other. If either of those values is a life total, the affected player gains or loses the amount of life necessary to equal the other value. Replacement effects may modify this gain or loss, and triggered abilities may trigger on it. A player who can't gain life can't be given a higher life total this way, and a player who can't lose life can't be given a lower life total this way (see rules 118.7-8). If either of those values is a power or toughness, a continuous effect is created setting that power or toughness to the other value (see rule 613.3b). This rule does not apply to spells and abilities that switch a creature's power and toughness.
April 27, 2018 · Dominaria
A spell or ability may instruct a player to exchange two numerical values. In such an exchange, each value becomes equal to the previous value of the other. If either of those values is a life total, the affected player gains or loses the amount of life necessary to equal the other value. Replacement effects may modify this gain or loss, and triggered abilities may trigger on it. A player who can’t gain life can’t be given a higher life total this way, and a player who can’t lose life can’t be given a lower life total this way (see rules 118.7–8). If either of those values is a power or toughness, a continuous effect is created setting that power or toughness to the other value (see rule 613.3b). This rule does not apply to spells and abilities that switch a creature’s power and toughness.