Unbounded Potential — ruling 1

If you cast this spell by paying its entwine cost, you will be able to proliferate the counters that you placed with the first mode.

Unbounded Potential — ruling 2

To proliferate, you can choose any permanent that has a counter, including ones controlled by opponents, and 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.

Unbounded Potential — ruling 3

You don't have to choose every permanent or player that has a counter, only the ones you want to add another counter 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.

Unbounded Potential — ruling 4

While proliferating, if you choose a permanent or player with multiple kinds of counters, the permanent or player gets another counter of each kind, not just one kind. This change from the original proliferate rules was introduced in a previous set.

Unbounded Potential — ruling 5

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.

Unbounded Potential — ruling 6

If a permanent has +1/+1 counters and -1/-1 counters on it, they're removed in pairs as a state-based action so that the permanent has only one of those kinds of counters (or none of either kind of counters) on it.

Unbounded Potential : règles, fonctionnement et interactions (MTG)

Unbounded Potential 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

Choose one — • Put a +1/+1 counter on each of up to two target creatures. • Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.) Entwine (Choose both if you pay the entwine cost.)

How it works : Unbounded Potential

Original English text — Wizards of the Coast / Scryfall

#1June 18, 2021· Wizards of the Coast
If you cast this spell by paying its entwine cost, you will be able to proliferate the counters that you placed with the first mode.
No other card is named in this ruling.
#2June 18, 2021· Wizards of the Coast
To proliferate, you can choose any permanent that has a counter, including ones controlled by opponents, and 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.
#3June 18, 2021· 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 another counter 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.
#4June 18, 2021· Wizards of the Coast
While proliferating, if you choose a permanent or player with multiple kinds of counters, the permanent or player gets another counter of each kind, not just one kind. This change from the original proliferate rules was introduced in a previous set.
No other card is named in this ruling.
#5June 18, 2021· 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.
#6June 18, 2021· Wizards of the Coast
If a permanent has +1/+1 counters and -1/-1 counters on it, they're removed in pairs as a state-based action so that the permanent has only one of those kinds of counters (or none of either kind of counters) on it.
No other card is named in this ruling.