How many poison counters does it take to lose with Poisonous?

Ten. Any player who accumulates ten or more poison counters loses the game immediately. This is true for poison counters from any source — Poisonous, Toxic, Infect, or older pre-keyword poison cards.

Does Poisonous trigger on non-combat damage?

No. Poisonous only triggers when the creature deals combat damage to a player. If the creature deals damage through an ability or spell rather than in the combat damage step, Poisonous does not trigger. This is the key rules distinction between the Poisonous keyword and many older poison cards like Marsh Viper, which triggered on any damage.

How many cards have the Poisonous keyword?

Just two: Virulent Sliver and Snake Cult Initiation, both from Future Sight (2007). Poisonous was always intended as a flag-planting mechanic, signalling that poison would return in a bigger form — which it did, first with Infect and later with Toxic.

What is the difference between Poisonous, Infect, and Toxic?

Poisonous deals normal combat damage and separately gives poison counters equal to its N value. Infect (from Scars of Mirrodin) replaces normal damage entirely — dealing damage to players as poison counters and to creatures as -1/-1 counters instead. Toxic (from Phyrexia: All Will Be One) deals normal combat damage and gives additional poison counters on top, similar in effect to Poisonous but with a distinct underlying rules framework.

Can you remove poison counters from a player?

Almost never. Poison counters are permanent in almost all game states — there is no general mechanic for removing them. The card Leeches (from Homelands) is one of the very rare exceptions. This is what makes poison strategies powerful: every counter you give an opponent stays there.

If a creature has two instances of Poisonous, do they both trigger?

Yes. According to CR 702.70b, if a creature has multiple instances of Poisonous, each triggers separately. So a creature with Poisonous 1 and Poisonous 2 would give a player 3 poison counters total from a single combat damage event.

Poisonous: MTG Keyword Mechanic Guide

There's something satisfying about a win condition that bypasses life totals entirely. Poisonous is one of Magic's oldest alternative paths to victory - a triggered keyword that loads poison counters onto opponents one combat at a time, racing toward the ten-counter threshold that means instant death.

It's a small mechanic with a big legacy, and understanding it means understanding a thread that runs from the earliest days of Magic all the way through to Phyrexia: All Will Be One.

What is Poisonous?

Poisonous is a triggered keyword ability. Whenever a creature with Poisonous deals combat damage to a player, that player gets a number of poison counters equal to the keyword's value - written as "Poisonous N" on the card.

Poison counters are a separate resource from life. Any player who accumulates ten or more poison counters loses the game immediately, regardless of how many life points they have left. Think of it like a second life bar - one that only goes down, never up, and that starts killing you the moment it hits ten.

Rules note: The "poisoned" condition simply means having one or more poison counters (CR 122). You don't need to track thresholds mid-game - the game ends automatically when any player reaches ten.

Rules

The official rules for Poisonous are straightforward, but there are a few edges worth knowing.

"Poisonous N means 'Whenever this creature deals combat damage to a player, that player gets N poison counters.'" - CR 702.70a

A few things to pay close attention to:

Combat damage only. Poisonous triggers exclusively on combat damage. If a creature deals damage some other way - through a spell or ability - Poisonous does not trigger. This is the key distinction separating Poisonous from many of the older pre-keyword poison cards.
Multiple instances stack separately. If a creature somehow has Poisonous 1 and Poisonous 2 (from different sources), each instance triggers independently, and the player takes 3 poison counters total from a single combat damage event. CR 702.70b is explicit on this.
Poison counters are not removed by damage prevention. Preventing the combat damage also prevents the Poisonous trigger, since there's no damage being dealt. But if damage goes through, the counters happen - they're a consequence of the damage, not damage themselves.

Poisonous vs. older poison cards

Before Poisonous was keyworded, Magic had a wave of creatures in the early sets - Marsh Viper, Pit Scorpion, Swamp Mosquito, and others - that dealt poison counters in text. Crucially, most of these triggered on any damage, not just combat damage.

When Poisonous was introduced in Future Sight, those older cards received no errata. Changing their wording would have changed how they functioned, which Wizards wisely avoided. So if you're playing with those older cards, they still work the way they always have - any damage, not just combat.

Poisonous vs. Toxic

Toxic, introduced in Phyrexia: All Will Be One (ONE), works differently from Poisonous in one important way: Toxic triggers based on combat damage dealt, but the poison counters are given in addition to that damage, and the Toxic value contributes to poison counters rather than replacing damage. Poisonous is purely additive on top of regular combat damage as well, but the underlying rules framework is distinct - Toxic is handled under CR 702.164 and is considered a separate mechanic.

In practice, both mechanics put poison counters on players who take combat damage. The distinction matters most if you're playing with older cards or mixing mechanics.

Strategy

Poisonous is a classic alternative win condition mechanic. The strategic logic is simple: you're running a second clock that opponents usually can't interact with directly. Most removal and life gain does nothing to slow the poison counter accumulation once damage is dealt.

Playing with Poisonous

The mechanic rewards evasion above almost everything else. A creature with Poisonous that gets blocked every turn is just a bad attacker. One with flying, unblockable, or deathtouch forces opponents into uncomfortable choices - take the counters, or trade away a blocker.

Virulent Sliver is the defining example here. In a Sliver deck, every creature on your board suddenly threatens poison counters on top of regular combat damage. The pressure compounds fast.

With only two cards printed carrying the Poisonous keyword itself, dedicated Poisonous strategies aren't really viable in any competitive format. Historically, poison strategies leaned on the broader pool of older poison cards and later shifted to Infect or Toxic when those mechanics appeared.

Playing against Poisonous

The most important thing to remember: poison counters don't go away. Unlike life totals, there's almost nothing in the game that removes poison counters from a player (the card Leeches is one of the very few exceptions). That means every time a Poisonous creature connects, you're permanently closer to ten.

Prioritise blocking and removing Poisonous creatures early. Don't let a Snake Cult Initiation-enchanted creature connect three times thinking you can recover - at Poisonous 3, that's three hits and you're done.

Notable cards

Poisonous has only ever appeared on two cards. That's not a typo - it really is just two.

Virulent Sliver ({G})

A 1/1 Sliver for one mana that gives every Sliver creature Poisonous 1. In a Sliver deck with any kind of board presence, this card turns every combat into a poison threat across multiple creatures. The power here is in the symmetry it creates between a go-wide Sliver strategy and a poison win condition. It's honestly a clever design - one cheap card that retrofits a whole tribe.

Snake Cult Initiation ({4}{B})

An Aura that enchants any creature and gives it Poisonous 3. Five mana is a real cost, but Poisonous 3 means only four successful hits to kill a player. Slap this on a creature with evasion and you're running a legitimate clock. It appeared as a timeshifted card in Future Sight (FUT), meaning it was printed in the future-card frame as a hint of things to come.

Lore aside: The timeshifted cards in Future Sight were Wizards' way of showing players possible futures for Magic design. Snake Cult Initiation wearing the Poisonous keyword was Mark Rosewater planting a flag - this mechanic space was coming back, even if the specific execution would evolve.

History

Poison as a concept in Magic is older than most players realise. The very first poison cards appeared all the way back in Legends (1994) and The Dark (1994), with creatures like Marsh Viper dealing poison counters through their rules text rather than a keyword.

The mechanic was actually designed during the development of Tempest (1997) under the name "poisonous," but it didn't make the cut for that set.

It finally surfaced as a keyword in Future Sight (FUT, 2007), where it appeared on exactly two cards - Virulent Sliver and the timeshifted Snake Cult Initiation. During Future Sight's design, the ability was internally called venom before settling on the printed name. Both of those working names give a sense of how Wizards was thinking about the flavour space.

The mechanic was explicitly intended as a signal. Mark Rosewater has described it as keyworded form of what poison had always done - a way of saying "poison is coming back in a bigger way." That bigger way arrived with Infect in Scars of Mirrodin (SOM, 2010), which combined the poison counter delivery with the power-modification mechanic, and became one of the most debated keywords in Modern's history.

Infect's own complications in competitive play meant the door wasn't closed on a simpler, cleaner poison keyword. That door opened again with Toxic in Phyrexia: All Will Be One (ONE, 2023), which reworked the core idea of Poisonous into a more nuanced mechanic that deals damage and poison counters simultaneously, rather than replacing normal damage.

Poisonous itself, sandwiched between pre-keyword poison cards, Infect, and Toxic, remains a small but historically meaningful mechanic - the explicit moment Wizards chose to formalise poison as a keyworded design space.