Viral Drake — ruling 1

To 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.

Viral Drake — ruling 2

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.

Viral Drake — ruling 3

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.

Viral Drake — ruling 4

An ability that triggers "Whenever you proliferate" triggers even if you chose no permanents or players while doing so.

Viral Drake — 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.

Viral Drake — ruling 6

If a permanent ever has both +1/+1 counters and -1/-1 counters on it at the same time, they're removed in pairs as a state-based action so that the permanent has only one of those kinds of counters on it.

Viral Drake : règles, fonctionnement et interactions (MTG)

Viral Drake 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

Flying Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.) : Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

How it works : Viral Drake

Original English text — Wizards of the Coast / Scryfall

#1February 4, 2023· Wizards of the Coast
To 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.
#2February 4, 2023· 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.
#3February 4, 2023· 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.
#4February 4, 2023· Wizards of the Coast
An ability that triggers "Whenever you proliferate" triggers even if you chose no permanents or players while doing so.
No other card is named in this ruling.
#5February 4, 2023· 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.
#6February 4, 2023· Wizards of the Coast
If a permanent ever has both +1/+1 counters and -1/-1 counters on it at the same time, they're removed in pairs as a state-based action so that the permanent has only one of those kinds of counters on it.
No other card is named in this ruling.