Batches of Effects
The bulk of the timing system is built on the concept of the batch. A batch of effects is composed of a series of effects, which can be spells, the abilities of permanents, or both. Each effect in the batch is played after the effect before it. A batch is never complete until both players are finished adding effects to it. Once a batch is complete, it starts to resolve in reverse order of how the effects were added to it (last in, first out). Each effect resolves fully before the next one starts to resolve. Once a batch has begun resolving, additional effects can't be added, and a new batch can't be started. If any effect in the batch assigns damage to any creatures and/or players, this is handled with a damage-prevention step before the next effect in the batch resolves.
Bob plays Incinerate, which deals 3 damage, on Sue's War Mammoth (3/3). Sue responds to the Incinerate with a Giant Growth, which gives the Mammoth +3/+3 until end of turn. Then, surprise! Bob plays a second Incinerate. When this batch begins resolving, it starts with the last effect that occurred, the second Incinerate, which deals 3 damage to the Mammoth. At this point, Sue intervenes with a Healing Salve, which prevents the damage. After that, resolution moves to the next effect, Giant Growth, which gives the Mammoth a toughness of 6. The last effect, Incinerate, deals 3 damage to the Mammoth, which isn't enough to kill it.
Each phase begins in a neutral state, when both players have the option of beginning a batch of effects. The active player decides first whether to do so; if she decides not to, the phase will end unless the opponent begins a batch of effects. Once the batch has finished resolving, the phase returns to a neutral state. This process is repeated until neither player begins a batch of effects.
Once during the main phase, the active player may play a land before deciding whether to start a batch of effects. If it's the active player's main phase and she hasn't attacked this turn, she may announce her intention to attack rather than announcing the end of the phase; if the opponent doesn't then start a batch, the attack begins. If the active player is in the neutral state during her main phase, and has not attacked, then she may announce intention to attack, rather than intention to end the phase. If the opponent responds by beginning a batch of effects, then the attack is aborted, and the active player can announce an attack again later in the turn. Otherwise, the attack begins. Once the attack is over, the main phase returns to the neutral state.
As explained earlier, whenever both players can or must do something, the active player gets the chance to do so first. This means that whenever there's an opportunity to start a batch, the active player decides first whether to do so. Once an effect is added to a batch, the active player decides first whether to respond with an effect, even if she was the one who added the most recent effect to the batch.
Most batches are composed solely of instants and abilities that are played as instants, as you can play these during most phases of either player's turn. During your main phase, however, you can start a batch with a sorcery or a spell that becomes a permanent.
Interrupts
Playing a spell or ability isn't just as simple as paying the costs and making any required choices. Doing these things activates the ability or casts the spell, and both players then get the chance to interrupt it. Interrupts are spells and abilities that target a spell or an effect with the intent of modifying or canceling it.
Interrupts played during the casting of a spell or use of an ability are built up into batches and can interrupt any casting, even if effects aren't generally usable at the time. These batches are constructed according to the normal rules for batches of effects, with one exception: the caster of the spell or effect being cast (not necessarily the active player) has priority in starting such a batch and in adding interrupts to it. There can be any number of batches of interrupts during the playing of a spell or effect. Interrupts can target only the spell or effect being cast.
Some interrupts counter the spell or effect being cast. In this event, the spell or effect is canceled and put into the graveyard. Costs paid for the spell or ability aren't recovered, including sacrificed permanents that are now in the graveyard and life that's been paid. A spell or effect that's countered becomes an illegal target for other interrupts, so any interrupts that targeted it and are waiting to resolve will fizzle with respect to that spell or effect. If, after a batch of interrupts has resolved, a spell or effect has been countered, the casting process of that spell or effect ends. Whoever played the countered spell or effect can now play another spell or effect as appropriate.
Bob plays a Fireball on Sue, paying enough to defeat her with it. Bob doesn't
intend to play any interrupts, but Sue wants to counter the Fireball, so she
begins a batch of Interrupts during its casting. She plays Hydroblast, which
counters a target spell if it's red (as the Fireball is). Bob responds to
Sue's spell by playing Deathlace, which will the change the Fireball to black.
Sue responds to the Deathlace by playing another Hydroblast.
Neither player wnats to play any more interrupts, so the batch starts resolving.
The second Hydroblast resolves and counters the Fireball. Thus the next two
effects, Deathlace and the other Hydroblast, fizzle when they resolve.
If a spell or ability is played and not countered by the time all interrupts (if any) have resolved, it's considered successfully cast. Any effects that trigger on it being cast are processed (see Specialized and Triggered Effects), and the spell or effect resolves at the appropriate time.
Mana sources can't be interrupted and therefore don't follow this process when used. Instead, they simply add the appropriate mana to your mana pool. Any effects triggered by the mana source's cost being paid, however, will function normally. For example, if using a mana source requires the sacrifice of a creature, any death effects will trigger normally after the mana is added to your pool.
Interrupts that target things other than spells or effects or that target nothing at all are played as if they were instants. This means they can only be added to (or begin) a normal batch of effects and can't be played during the casting of a spell or ability. This will result in certain spells of type "Interrupt" being played differently depending on what they're targeting.
Hydroblast is played on a "target permanent or spell." It can target a permanent only if played as an instant and can target a spell only if played as an interrupt.
Specialized and Triggered Effects
Some spells and abilities can be played only in certain situations, and some abilities take effect only when a certain situation occurs. For example, regeneration effects may be used only when a creature is headed for the graveyard. These spells and abilities are collectively referred to as specialized effects, because they're applicable only during specific, or special, situations. (Damage-prevention effects, like Healing Salve, follow slightly different rules and aren't considered specialized effects.) Triggered effects are a subset of specialized effects that occur (trigger) automatically under certain conditions.
Death Ward is a specialized effect that regenrates its target. The ability of Aladdin's Lamp (draw X cards and keep one) is a specialized effect that's used when you'd normally draw a card.
Underworld Dreams (deals damage whenever its target draws a card) and Iron Star (usable only when a red spell is successfully cast) are triggered effects.
If an effect causes the target of Underworld Dreams to draw any cards, the Dreams doesn't deal any damage until the effect has finished resolving. On the other hand, Aladdin's Lamp is used during the resolution of an effect that causes a player to draw cards.
If both players have specialized effects to play, the active player plays all of hers first. The effects are played one at a time, with every effect resolving before the next is played. As soon as the active player is finished, the other player does the same thing.
A triggered effect happens automatically if there's no cost associated with it, regardless of whether you want it to. If a triggered effect does have a cost, you're not required to use it, but if you choose to use it you must do so following the event that triggered it or not at all. Triggered effects go off whenever an appropriate event happens, even if the source of the effect is no longer in play when it's time to resolve the effect.
Sue's Soul Net allows her to spend 1 to gain 1 life whenever a creature is put into the graveyard from play. Sue must decide whether to pay 1 for 1 life. If she doesn't pay at that point, she can't change her mind and pay later. Bob animates the Soul Net, making it a 1/1 creature, and enchants it with Creature Bond. Bob then deals 1 damage to the Sould Net with his Prodigal Sorcerer. Neither player prevents the damage or regenerates the Soul Net, so it's put into the graveyard. Two effects trigger on the Sould Net being put into the graveyard: Creature Bond's and Soul Net's. Creature Bond's takes play automatically, dealing 1 damage to Sue. Sue may also pay 1 to gain 1 life with the Soul Net's ability, even though the Soul Net is already in the graveyard.
Whenever an effect generates both triggered effects and damage prevention, the triggered effects are handled first.
Phase Structure
Whenever a player takes a turn, she goes through six basic phases: untap, upkeep, draw, main, discard, and cleanup. Each phase serves a special purpose necessary to the continuity and flow of the game. The draw phase, for instance, requires the active player to add a new card to her hand. For more details about how the phases differ, see The Full Turn Sequence.
Fast effects may be played during all the phases except for untap and cleanup. However, every phase goes through the same basic steps:
- Process all effects that occur at the beginning of the phase.
- The bulk of the phase, which can have any number of batches.
- Process all effects that occur at the end of the phase.
- Check for mana burn (see Mana and the Mana Pool).
- Check life totals.
The typical phase effect is an upkeep effect such as Unstable Mutation's. This effect puts a -1/-1 counter on the enchanted creature, paid during its controller's upkeep. As long as the enchanted creature remains in place, the creature's controller puts a counter on it during each of her upkeep phases.
If more than one effect happens at the beginning or end of a phase and the order of these effects matters, they're played in the same way as specialized effects.
There are ways to avoid dealing with a phase effect. First, a phase effect prohibits you from ending a phase only as long as the effect is in play, so if you remove its source, you can ignore the phase effect. The abilities of artifacts shut off while the artifacts are tapped--one way of avoiding the phase effect of an artifact. Finally, if there's no legal target for the effect, you can end the phase without dealing with it.
Ernham Djinn is a creature with an upkeep effect that requires you to to give forestwalk to a target creature your opponent controls. You can avoid this phase effect by (1) taking the Djinn out of play, or (2) by eliminating all of your opponent's creatures. The second approach, however, won't work if your opponent produces more creatures before you end your upkeep phase.
Certain permanents have a cost paid during a certain phase. These phase costs are generally optional but carry a penalty for nonpayment. If a permanent has more than one phase cost, they combine into a single cost. If the individual costs would have been paid at different times, the combined cost is considered paid at the last such time. Each phase cost can be paid only once during the phase. Paying a phase cost (or refusing to do so) is played as an instant. Permanents with phase costs can't use optional abilities (such as those with activation costs) until the phase cost effect has resolved, regardless of whether you paid the cost. Unlike phase effects, phase costs always have to be handled, even if the permanent is tapped.
Energy Flux gives all artifacts in play a phase cost of 2, to be paid during upkeep. If an artifact's cost isn't paid, that artifact is buried. If two Energy Fluxes are in play, they combine to give each artifact a total cost of 4. If an artifact has an activated ability it can't be played until the "pay the phase cost or decline to do so" effect has resolved; thus, an artifact that provides mana can't be used to pay for its own upkeep cost.