Mechanics

The metal plane of Mirrodin is now a world at war. The insidious influence of Phyrexia has been incubating for years within the plane's mana core. In Scars of Mirrodin, the people of Mirrodin began to suspect something was wrong with their world as the Phyrexians made final preparations for war. Now, in Mirrodin Besieged, Phyrexian horrors boil out of the ground to assault the plane's unaltered inhabitants, the Mirrans.

Both sides have armed themselves with new weapons and tactics in a battle that will decide the fate of the entire plane. Will the armies of the uninfected keep Mirrodin pure, or will hordes of "compleated" monstrosities forge a new Phyrexia on Mirrodin?

Battle Cry

The Mirrans know that their survival depends on unity, and the new battle cry mechanic lets your creatures attack as a team to devastating effect.

When a creature with battle cry attacks, each other attacking creature gets +1/+0. For example:

• If you attack with just an Accorder Paladin, there won't be any other attacking creatures to get the bonus.
• If you attack with two Accorder Paladins, each one will pump the other. When their triggers resolve, each one will get +1/+0.
• If you attack with two Accorder Paladins and a 1/1 Myr artifact creature token, each Accorder Paladin will pump the other Paladin and the Myr. When the triggers resolve, each Paladin will get +1/+0 as before, and the Myr token will get a total of +2/+0. That's 11 power on the attack!

Battle cry even helps creatures you don't control that attack at the same time as creatures you control that have battle cry—for example, creatures controlled by your teammate in Two-Headed Giant.

A creature that enters the battlefield tapped and attacking before a battle cry ability resolves will get the bonus. For example, say you have Hero of Bladehold, the Mirran-aligned Prerelease promo card for Mirrodin Besieged:

Hero of Bladehold has two triggered abilities—battle cry, and a second triggered ability that puts Soldier creature tokens onto the battlefield tapped and attacking. Because you control both abilities, you get to choose the order in which you put them on the stack (along with any other triggered abilities you control that are triggering at the same time, such as other battle cry abilities). If you put the token-making ability on the stack last, it will resolve first, and the tokens will be there to get the bonus from Hero of Bladehold's battle cry (and any other battle cry abilities you put on the stack before the token-making ability).

Metalcraft

The returning ability word metalcraft gives you a bonus for controlling three or more artifacts. That bonus might be a keyword such as flying, increased power and toughness, or something unique.

As long as you control three or more artifacts, Razorfield Rhino gets +2/+2. As soon as you don't, it loses the bonus. So if a pumped-up Razorfield Rhino takes 4 damage and then your third artifact leaves the battlefield later in the turn (or at the same time, such as in combat), Razorfield Rhino will also be destroyed.

Some cards with metalcraft abilities, such as Razorfield Rhino, are themselves artifacts. They count themselves, so as long as you control two other artifacts (and Razorfield Rhino doesn't stop being an artifact somehow), your Rhino will get the bonus. Other cards with metalcraft abilities, such as Carapace Forger from Scars of Mirrodin, are not artifacts, and require three other artifacts (unless they become artifacts somehow, such as through the Scars of Mirrodin card Liquimetal Coating).

Living Weapon

While the Mirrans are busy honing their tactics and forging new weapons of war, the Phyrexians have unveiled twisted new creations of their own. When you open a Mirrodin Besieged booster pack, you might find a token card that looks like this:

A 0/0 token! You might wonder what good that is, why anyone would want such a thing. The answer has to do with the Phyrexians' new living weapon mechanic.

When an Equipment with living weapon enters the battlefield, its controller puts a 0/0 black Germ creature token onto the battlefield and attaches the Equipment to it. A 0/0 creature on its own would immediately be put into its owner's graveyard for having 0 or less toughness, but with Flayer Husk attached to it, the Germ token will live to fight as a healthy 1/1. Other Equipment cards with living weapon give different power and toughness increases, but all of them give at least 1 point of toughness.

After the Germ token dies, the Equipment will stick around as usual, ready to be equipped to another creature you control. But if you're feeling especially Phyrexian, you don't even have to wait that long! As with other Equipment, you can activate Flayer Husk's equip ability any time you could cast a sorcery to attach it to another target creature you control. If you do this successfully while the Germ token is still on the battlefield (and the Germ token isn't getting another toughness bonus, such as from Marshal's Anthem or Accorder's Shield), the Germ token will be put into its owner's graveyard for having 0 or less toughness.

Whether you need a creature or an Equipment, living weapon has you covered. (Just don't ask what it has you covered in.)

Infect

In addition to their new living weapons, the Phyrexians still employ the potent threats of poison counters and -1/-1 counters, both of which are handed out most prominently in this set by the returning infect mechanic.

In Scars of Mirrodin, infect appeared exclusively in black, green, and artifacts, and that's still where you'll find most creatures with infect in Mirrodin Besieged. But a few Phyrexian infiltrators have appeared even in the solidly Mirran-aligned color of white.

As you might recall, creatures with infect deal damage to creatures and players in the form of -1/-1 counters and poison counters, respectively. So what does that mean, exactly?

When a creature with infect deals damage to a player, the player doesn't lose any life as a result of the damage—he or she gets that many poison counters instead. If a player ever has ten or more poison counters, that player loses the game.

When a creature with infect deals damage to another creature, the -1/-1 counters remain on the creature indefinitely. They're not removed if the creature regenerates or the turn ends. A creature with 0 or less toughness is put into the graveyard, even if it's indestructible or can regenerate.

Infect applies to any damage, not just combat damage—so if you can somehow give your Prodigal Pyromancer infect, its ability will deal damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.

Damage from a source with infect is damage, even though it does something different from other damage. Lifelink, deathtouch, and abilities that trigger when a creature deals damage will all work as normal, and the damage can be prevented or redirected just like any other damage.

Damage from a source with infect affects planeswalkers normally.

"Poisoned"

In Mirrodin Besieged, you may encounter the new rules term poisoned.

A player is poisoned as long as he or she has at least one poison counter. It doesn't matter how many poison counters that player has; a player either is poisoned or isn't, and Septic Rats either gets +1/+1 when it attacks or doesn't.

Proliferate

Proliferate is a returning keyword action that lets the Phyrexians spread their twisted infection. To proliferate, choose any number of players and/or permanents that each have at least one counter of any type. Each player chosen gets a counter of a kind that player has (so far, poison counters are the only counters players can get). Put a counter on each permanent chosen this way of a kind that permanent already has. You only get to put one counter on each permanent this way, even if that permanent has multiple kinds of counters on it.

So if a creature already has one or more -1/-1 counters on it, you can put another one on it when you proliferate. If an artifact already has one or more charge counters on it, you can put another charge counter on it, but you can't put a charge counter on an artifact that doesn't have one already. You can even choose to put more -1/-1 counters on your opponents' creatures while leaving your own creatures with -1/-1 counters on them alone, or give your opponent a poison counter without giving yourself one even if you both already have poison counters.

Mirrodin Besieged features a number of new cards that proliferate. A few of them, like Spread the Sickness, are instants or sorceries with targets.

If the creature you target with Spread the Sickness is no longer on the battlefield when Spread the Sickness would resolve, the spell will be countered instead, and you won't get to proliferate. If the spell does resolve, proliferating isn't dependent on actually destroying the creature. Even if the creature regenerates or is indestructible, you'll still get to proliferate.