Damage Prevention
Damage prevention can occur following the resolution of an effect or following a damage-dealing step. All of the damage dealt during a damage-dealing step or during the resolution of an effect is organized into "packets" of damage, with one packet for each creature or player that the creature or effect assigned damage to. Each packet records how much damage was assigned to that creature or player, the color and other characteristics of the source of damage, and so on.
Mana Clash is a sorcery that requires two players to start flipping coins and deals 1 damage to a player every time one of his coins comes up tails. This spell will generate, at most, two packets of damage (one for each player), for an amount of damage equal to the number of times that player flipped a coin that came up tails.
During damage prevention, players may use effects that prevent or redirect damage and play effects that are usable only when a creature or player is damaged. Such effects target the packets of damage they prevent, redirect, or otherwise act upon. If all of the damage in a packet is prevented, the packet of damage disappears and is no longer a valid target. Side effects of damage trigger on the corresponding packet successfully dealing its damage, so preventing all of that packet's damage will eliminate the side effect.
As damage prevention begins, effects that automatically reduce damage by or to a certain amount take effect and prevent the new damage as appropriate. Such effects are also applied to any new damage generated during the step. Side effects of damage, and effects that automatically redirect damage, don't apply until the end of damage prevention, and then they apply only to unprevented damage. After damage prevention, any creatures with lethal damage are put into the graveyard (although effects such as regeneration may be used normally). If any effects automatically redirected damage or any side effects generated new damage, another damage prevention step begins as this one ends.
Bob attacks Sue with two Grizzly Bears, one of which Sue has enchanted
with Backfire, which will deal 1 damage to Bob for each 1 damage the
enchanted Bears deals to Sue. Sue lets the enchanted Bears through and
blocks the other with her Hypnotic Specter. At the end of damage
prevention, the enchanted Bears and the Specter have dealt 2 damage
to each other and the second Bears has dealt 2 damage to Sue. The
Backfire triggers, dealing 2 damage to Bob, so the damage-prevention
step continues. But first the current step ends, so the Specter and the
Bears it's blocking are killed. Now there's a step to handle the
Backfire damage.
Note that if Bob or Sue wants to regenerate the Specter or the Bears
or use effects such as Soul Net, they'll do so before the second
step begins.
Note that if Bob or Sue wants to regenerate the Specter or the Bears or use effects such as Soul Net, they'll do so before the second step begins.
Effects played during damage prevention are played in batches and follow the normal rules for such. There can be any number of batches during the step. New damage generated during the step is absorbed into the current damage-prevention step rather than starting a new one.
Certain spells and abilities can have one of several effects, only some of which are legal during damage prevention. Such spells and abilities must be played differently depending on whether they're being played during damage prevention.
During damage prevention, Healing Salve can be used only to prevent damage; outside of damage prevention, it can be used only to gain life. Although it reads "prevent up to 3 damage," it can't be played outside damage prevention to prevent 0 damage.
Instants that coincidentally let a player or creature avoid or survive damage aren't legal during this step.
Unsummon can't be played during damage prevention. Although it returns the target creature to its owner's hand, causing that creature to avoid any damage, Unsummon doesn't specifically interact with damage and thus isn't legal during this step.
Giant Growth, which gives its target +3/+3 until end of turn, can't be played during damage prevention either. Even though its increased toughness might allow the target creature to survive damage it's taken, the spell won't prevent damage and therefore can't be played in this step.
Beginning a Duel
Each player begins the game with a deck of at least forty cards, which compose his or her library. Before play begins, each player shuffles his or her deck and then offers it to the opponent, who may shuffle and/or cut it. Next, one player decides who will play first and who will draw first; whoever takes the first turn of the game skips the draw phase for that turn. If the players have just finished a game, whoever lost that game decides who plays first; if the game was a draw, whoever decided who went first in that game does so again. If this is the first game in a series, determine randomly who decides.
Once the players know who'll be playing first and who'll be drawing first, they draw their initial hands of seven cards each. When both players are ready, play begins. Each player starts with 20 life.
The Full Turn Sequence
Fast effects are legal during every phase unless otherwise noted.
Untap: No fast effects are allowed. As a phase effect, all of your permanents untap simultaneously. Any choices you might be required to make about what to untap are made at the beginning of the phase.
Upkeep: Most phase costs and phase effects occur during this phase. Additionally, certain permanents may have untap costs that are paid during or at the end of upkeep. Untap costs follow the same rules as phase costs but are optional; that is, there's no penalty for not untapping something. Additionally, untap costs paid "during upkeep" rather than "at end of upkeep" may be paid more than once over the course of upkeep.
Draw: Draw a card as a phase effect. Each effect that instructs you to draw more cards is treated as another phase effect.
Howling Mine is an artifact that instructs each player to draw an additional card during his or her draw phase. Each Mine thus gives each player another phase effect of "draw one card." Each of these phase effects is played as an individual "instant."
Main: The active player may play spells and abilities of any kind, including non-fast effects such as artifact spells, enchantment spells, sorcery spells, and summon spells. Additionally, the active player can play one land and make one attack (non-fast effects aren't allowed while a player is attacking). Playing land, attacking, and playing spells can be done in any order.
Discard: At the end of this phase, check to see if you have more than seven cards in your hand. If you do, discard down to seven.
Cleanup: No fast effects are allowed. During this phase, all damage dealt to permanents this turn wears off; at the same time, all effects that last until end of turn wear off. All "at end of turn" effects occur at the end of this phase.
Note that while fast effects aren't allowed, specialized effects or damage prevention may be called for, especially as a result of "at end of turn" effects. If an effect played at this time lasts "until end of turn," it simply takes effect as it resolves and then ends, as you've already reached the end of the turn. If such effects lead to more "at end of turn" effects, resolve those effects afterwards. Repeat this cycle as necessary.
The Attack
When the active player has the chance to start a batch of effects during the main phase, he may decline to do so and instead announce his intention to attack. He can attack only his opponent, not himself or any specific creatures. His opponent may abort the attack by starting a batch of instants or interrupts. If the attack is aborted, the active player may try again later in the main phase.
A player can begin an attack only once during the main phase of his turn, although he can attempt to attack more than once if needed. If the active player controls any creatures that are required to attack, he can't end the main phase without having attacked. As soon as the attack is complete, the main phase of the player's turn resumes. During the attack phase, effects are legal only as noted in the steps outlined here. Effects that apply to damage dealt "in combat" apply only to damage assigned by creatures during the damage-dealing steps, not to damage from fast effects used during the attack. Non-fast effects can't be played at all, even though the attack happens during the main phase.
During the main phase, the active player announces the attack. Assuming the opponent doesn't abort the attack by playing effects, the main phase is put on hold to begin the attack. Players check for mana burn (see Mana and the Mana Pool,") and check their life totals before the attack actually begins. Once the attack begins, fast effects aren't legal until the second step, so if the opponent wants to play an effect that will affect how attackers are declared, she must do so by aborting the attack and playing the effect during the main phase.
Creatures involved in combat are either attacking creatures or blocking creatures, so this is the only time when spells or abilities that target such creatures can be played. Some events take a creature out of combat, specifically a change in controllers, regeneration, or ceasing to be a creature. Simply tapping or untapping a creature doesn't remove it from the combat. A creature that's removed from combat is no longer an attacking or blocking creature and won't deal or receive damage later in the combat. Creatures removed from combat don't untap as a result of their removal.