Contagion Engine — ruling 1

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.

Contagion Engine — ruling 2

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

Contagion Engine — ruling 3

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.

Contagion Engine — ruling 4

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.

Contagion Engine — ruling 5

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.

Contagion Engine — ruling 6

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.

Contagion Engine — ruling 7

Players can't respond between the first and the second proliferate actions.

Contagion Engine — ruling 8

As Contagion Engine's activated ability resolves, you'll complete an entire proliferate action, then you'll complete a second proliferate action. You may choose different players and/or permanents, or different counters on those permanents, when you proliferate the second time.

Contagion Engine : règles, fonctionnement et interactions (MTG)

Contagion Engine 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

When this artifact enters, put a -1/-1 counter on each creature target player controls. , : Proliferate twice. (Choose any number of permanents and/or players, then give each another counter of each kind already there. Then do it again.)

Complete guide

Contagion Engine is a powerhouse artifact that functions both as a targeted board wipe and a massive engine for counter-based strategies. By weakening an opponent's forces and then doubling down on your own advantages, it can quickly tilt the game in your favor. This colorless artifact fits into any deck looking to exploit counters of any variety.

Shrinking the Opposition

When Contagion Engine enters the battlefield, you choose a target player, and every creature they control receives a -1/-1 counter. This is a triggered ability that targets a player, not the creatures themselves, allowing you to place counters on creatures with Hexproof or Shroud. Note that if a creature has both a +1/+1 counter and a -1/-1 counter, they are removed in pairs as a state-based action until only one type remains.

Double Proliferation

The second ability allows you to pay four mana and tap the Engine to proliferate twice. To proliferate, you choose any number of permanents or players that already have counters and give them another counter of each kind already there. Because this ability says 'twice,' you perform this entire process, then immediately perform it again. You may choose different targets or the same ones for the second proliferation.

Timing and Responses

Players can respond to the activation of the Engine, but they cannot respond between the first and second proliferate actions. Once the ability starts resolving, you make your choices for the first proliferation, then the second, and no player can cast spells or activate abilities in the middle of this process. If a permanent has multiple kinds of counters, you must add one of each kind if you choose to proliferate it.

When to Deploy

Deploy Contagion Engine when your opponent has a wide board of small creatures to clear them out instantly, or when you have established permanents with powerful counters like loyalty, +1/+1, or charge counters. It is particularly effective in the late game where you have the mana to activate its ability the same turn it enters.

Interaction examples

Generating Extra Mana

Gilded Lotus

If you have a Gilded Lotus on the battlefield, you can tap it to add three mana of any one color to your mana pool. While Gilded Lotus itself doesn't use counters, it provides the significant mana required to activate Contagion Engine's ability repeatedly over several turns.

Managing Combat Math

Vanquisher's Banner

Suppose you control Vanquisher's Banner naming 'Human.' Your Humans get +1/+1 from the static ability. If an opponent targets your Humans with Contagion Engine's triggered ability, they receive -1/-1 counters. These counters will stay on your creatures and effectively cancel out the static buff from the Banner. If you then proliferate those -1/-1 counters, your creatures will continue to shrink regardless of the Banner's boost.

Step-by-Step Activation

1. You pay four mana and tap Contagion Engine. 2. Upon resolution, you choose any number of permanents/players with counters. 3. Each chosen target gets one additional counter of each type it already has. 4. You immediately repeat this process, potentially choosing the same targets to add a second set of counters. For example, a creature with one -1/-1 counter will end up with three -1/-1 counters total.

Guide written with AI from the official text and rulings. Official English text prevails.

How it works : Contagion Engine

Original English text — Wizards of the Coast / Scryfall

#1February 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.
#2February 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.
#3February 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.
#4February 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.
#5February 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.
#6February 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.
#7January 1, 2011· Wizards of the Coast
Players can't respond between the first and the second proliferate actions.
No other card is named in this ruling.
#8January 1, 2011· Wizards of the Coast
As Contagion Engine's activated ability resolves, you'll complete an entire proliferate action, then you'll complete a second proliferate action. You may choose different players and/or permanents, or different counters on those permanents, when you proliferate the second time.
No other card is named in this ruling.