Expansion Algorithm

X generic mana one blue mana Sorcery

Proliferate X times. (To proliferate, choose any number of permanents and/or players, then give each another counter of each kind already there.)

"When you find an equation that works, all that's left is finding its many applications." —Zimone

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Showing Secrets of Strixhaven Commander#19

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Expansion Algorithm rulings

2026-03-20
You don't have to choose every permanent or player that has a counter—only the ones you want to add counters to. Since "any number" includes zero, you don't have to choose any permanents at all, and you don't have to choose any players at all.
2026-03-20
If you proliferate multiple times, you don't have to choose the same set of players and/or permanents to get additional counters each time.
2026-03-20
When you proliferate, you can choose any permanent that has a counter, including ones controlled by opponents. You can choose any player who has a counter, including opponents. You can't choose cards in any zone other than the battlefield, even if they have counters on them.
2026-03-20
Players can respond to a spell or ability whose effect includes proliferating. Once that spell or ability starts to resolve, however, and its controller chooses which permanents and players will get new counters, it's too late for anyone to respond.
2026-03-20
If a player or permanent has more than one kind of counter on it, and you choose for it to get additional counters, it must get one of each kind of counter it already has. You can't have it get just one kind of counter it already has and not the others.
2026-03-20
While proliferating multiple times, players can't respond between proliferating the first time and proliferating the second time, and so on.

Expansion Algorithm keyword rules

Proliferate Rule 701.27

To proliferate means to choose any number of permanents and/or players that have a counter, then give each one additional counter of each kind that permanent or player already has.

In a Two-Headed Giant game, poison counters are shared by the team. If more than one player on a team is chosen this way, only one of those players can be given an additional poison counter. The player who proliferates chooses which player that is. See rule , “Two-Headed Giant Variant.”