Mirrodin Besieged (MBS): Set Guide

The war for Mirrodin was never going to end quietly. Mirrodin Besieged arrived on February 4, 2011, and dropped players right into the middle of a civilisational conflict - the Mirran resistance fighting to survive against a Phyrexian invasion that had already won most of the plane. It's the second set in the Scars of Mirrodin block, the 54th Magic expansion, and one of the most thematically cohesive sets Wizards had produced up to that point. Every card tells you whose side it's on.

What is Mirrodin Besieged?

Mirrodin Besieged (MBS) is a 155-card expansion released on February 4, 2011. It sits between Scars of Mirrodin (2010) and New Phyrexia (2011) in the Scars of Mirrodin block, and it carries the full weight of that middle-chapter tension - the outcome of the war is unresolved, and the set design reflects exactly that uncertainty.

The set came with two event decks, continuing Wizards' practice of offering ready-to-play competitive products alongside the main release.

Themes and mechanics

The single most important design decision in MBS is the Mirrored Pairs theme. Cards from the Mirran and Phyrexian factions are deliberately designed to echo each other, giving you a visual and mechanical sense of two armies meeting in the middle. Peace Strider and Pierce Strider share a body and a cost, but opposite effects. Mirran Crusader and Phyrexian Crusader are protection mirrors of each other - one shielded from black and green, one from white and green. Even iconic artifacts from the original Mirrodin block got the treatment: Blightsteel Colossus riffs on Darksteel Colossus, and Inkmoth Nexus is a Phyrexia-touched answer to Blinkmoth Nexus. Viridian Corrupter echoes Viridian Shaman - same role, corrupted purpose.

This mirroring isn't just flavour. It's a mechanical argument: Phyrexia doesn't destroy Mirrodin so much as replace it, piece by piece.

Returning mechanics

Four mechanics carry over from Scars of Mirrodin:

• Metalcraft - rewards controlling three or more artifacts, fitting for a metal plane.
• Imprint - exiles a card onto an artifact to modify its function.
• Proliferate - adds a counter of each kind already present on any permanent or player you choose. In a set with both poison counters and charge counters everywhere, this is as powerful as it sounds.
• Infect - creatures deal damage in the form of -1/-1 counters to creatures and poison counters to players. Ten poison counters and your opponent loses, regardless of life total.

New mechanics: Battle Cry and Living Weapon

Each faction gets a keyword of its own, and the contrast between them tells you everything about how each side fights.

Battle Cry is the Mirran keyword. When a creature with Battle Cry attacks, every other attacking creature gets +1/+0 until end of turn. It's a rallying cry - a single champion inspiring the troops around them. It rewards going wide, attacking as a team, and building a board before committing.

Living Weapon is the Phyrexian keyword, and it's genuinely strange in the best way. Every Equipment with Living Weapon creates a 0/0 black Germ creature token when it enters the battlefield, then immediately attaches itself to that token. The Equipment boosts the Germ enough to make it relevant - you always have a body for your sword, even if you have no other creatures. It's self-sufficient in a way that feels deeply Phyrexian: the weapon generates its own host.

A small rules addition

MBS introduced the term "poisoned" as a formal rules concept. A player is poisoned if they have one or more poison counters. This sounds minor, but it matters for cards that check whether a player has poison counters - previously the rules lacked a clean shorthand for that state.

Limited and Draft

Draft with MBS was built around the faction divide in a very literal sense. The Mirran side leans on Battle Cry and go-wide aggro strategies - pump your team, attack early and often, close games before your opponent stabilises. The Phyrexian side leans on Infect and Living Weapon, threatening a completely different win condition that ignores life totals entirely.

One of the more interesting tensions in MBS Limited is that the two poison-based win conditions (Infect beatdown vs. Proliferate-fuelled attrition) can pull a Phyrexian drafter in different directions. Pure Infect wants to end the game fast with a single large creature. Proliferate wants to spread counters slowly and grind. Mixing those strategies carelessly tends to produce a deck that doesn't do either well.

Battle Cry rewards drafting multiple creatures at the same cost and going wide - two-drops into three-drops into a Battle Cry attacker felt like the clean Mirran draft line. Living Weapon Equipment picks up in value if you're already thin on creatures, since each piece brings its own body.

The Mirrored Pairs also create interesting pick decisions: when both versions of a card exist in the same draft pool, reading which one your table is taking tells you which faction is open.

Notable cards and impact

Blightsteel Colossus immediately became one of the most feared reanimation and cheat targets in the game - infect plus trample means ten poison counters can arrive in a single unblocked swing, and it shuffles back into the library if it would go to a graveyard. Inkmoth Nexus became a staple in multiple Infect strategies across Modern and Legacy, valued for being a land that turns into an infect flier only when needed, making it very difficult to interact with at sorcery speed.

Mirran Crusader found a home in white aggro and midrange strategies for years, particularly in formats where black and green removal is dominant - it's essentially a creature that ignores the two most common ways to answer it.

Phyrexian Crusader filled a similar role in more controlling or Infect-based strategies, especially given that first strike and infect is a genuinely dangerous combination in combat.

Green Sun's Zenith - a card that searches your library for a green creature and puts it directly onto the battlefield - proved powerful enough to eventually be banned in Modern (March 2012) and remains restricted in some formats. its interaction with the broader Scars block environment made it particularly difficult to contain.

Lore and setting

Mirrodin Besieged takes place on Mirrodin, the artificial metal plane created by the golem Karn. By this point in the story, Phyrexia has been quietly growing beneath the surface for years - and the invasion is now open and overwhelming. The Mirran people are fighting back, but the numbers are against them.

The Mirrored Pairs theme isn't just design elegance - it's a lore statement. Every Mirran institution, creature, and tool has a Phyrexian counterpart that has replaced or subverted it. Viridian elves who once shaped nature to protect the plane now spread corruption instead. Colossuses that were once near-indestructible symbols of Mirrodin's strength have been rebuilt as Phyrexian weapons.

The set ends with the outcome still uncertain - that was deliberate, building toward New Phyrexia and its devastating conclusion. The marketing campaign around MBS and New Phyrexia actually asked players to fight for their faction, tracking which side was winning across event results. The answer, ultimately, was Phyrexia. The set name "New Phyrexia" was itself a spoiler once it leaked.

Lore aside: The tension between the two factions is reflected right down to the card back variants and booster packaging for this block - Wizards leaned hard into the war framing as a marketing and design concept, and MBS is where that framing reached its peak before the conclusion.

Set legacy

Mirrodin Besieged is remembered fondly as one of the tighter designs of the early 2010s. The Mirrored Pairs concept gave the set a mechanical identity that was immediately readable, even for new players - you could pick up a booster, see two similar cards, and immediately understand the story it was telling.

The Living Weapon mechanic didn't go on to become a format staple in the way Proliferate or Infect did, but it's a genuinely inventive piece of design: Equipment that supplies its own creature solves one of the classic problems with the Equipment card type. I'd be surprised if we never see it return.

Battle Cry, by contrast, has been largely quiet since MBS - it's a clean, readable mechanic that sits in white and red's identity space, and I'd expect Wizards to revisit it eventually.

The bigger legacy is probably Inkmoth Nexus and Blightsteel Colossus, two cards that have cast long shadows over eternal formats. Nexus in particular became the Infect land - cheap, evasive, hard to interact with, and appearing in everything from Modern Infect to Legacy and Vintage Affinity-adjacent strategies.

The Scars of Mirrodin block as a whole is often cited as a high point for mechanical cohesion and flavour integration, and MBS - the middle chapter where the stakes are highest and the outcome is still uncertain - might be its best expression of both.