Expansion Algorithm — ruling 1

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.

Expansion Algorithm — ruling 2

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.

Expansion Algorithm — ruling 3

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.

Expansion Algorithm — ruling 4

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.

Expansion Algorithm — ruling 5

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.

Expansion Algorithm — ruling 6

While proliferating multiple times, players can't respond between proliferating the first time and proliferating the second time, and so on.

Expansion Algorithm : règles, fonctionnement et interactions (MTG)

Expansion Algorithm is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

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

How it works : Expansion Algorithm

Original English text — Wizards of the Coast / Scryfall

#1March 20, 2026· Wizards of the Coast
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.
No other card is named in this ruling.
#2March 20, 2026· Wizards of the Coast
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.
No other card is named in this ruling.
#3March 20, 2026· Wizards of the Coast
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.
No other card is named in this ruling.
#4March 20, 2026· Wizards of the Coast
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.
No other card is named in this ruling.
#5March 20, 2026· Wizards of the Coast
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.
No other card is named in this ruling.
#6March 20, 2026· Wizards of the Coast
While proliferating multiple times, players can't respond between proliferating the first time and proliferating the second time, and so on.
No other card is named in this ruling.