Phasing

Phasing is a keyword ability which causes permanents to move between the "in-play" zone and the "phased-out" zone. This is the only way in which a creature can enter or leave the "in-play" zone without triggering abilities that trigger when permanents enter or leave play. It is also the only way a permanent can leave play and then re-enter play while "remembering" it is the same permanent.

All tournament-legal cards with phasing were printed during Mirage Block.

From the Comprehensive Rules

• 502.15. Phasing
  • 502.15a Phasing is a static ability that modifies the rules of the untap step.
  • 502.15b During each player’s untap step, before the active player untaps his or her permanents, all permanents with phasing the player controls phase out. Simultaneously, all objects that had phased out under that player’s control phase in. (See rule 217.8, “Phased Out,” and rule 302.1.)
  • 502.15c If an effect causes a player to skip his or her untap step, the phasing event simply doesn’t occur that turn.
  • 502.15d Permanents phasing in or out don’t trigger any comes-into-play or leaves-play abilities, and effects that modify how a permanent comes into play are ignored. Abilities and effects that specifically mention phasing can modify or trigger on these events, however. (Because no player receives priority during the untap step, any abilities triggering off of the phasing event won’t go onto the stack until the upkeep step begins.)
  • 502.15e When a permanent phases out, all damage dealt to it is removed.
  • 502.15f A card that returns to play from the phased-out zone is considered the same permanent it was when it left. This is an exception to rule 217.1c, which stipulates that a permanent “forgets” its previous existence when it changes zones.
  • 502.15g Effects with limited duration and delayed triggered abilities that specifically reference a permanent will be unable to further affect that permanent if it phases out. However, other effects that reference the permanent (including effects with unlimited duration) can affect the permanent when it returns to play.
    • Example
      A creature is affected by Giant Growth and then phases out during the same turn. If the creature phases back in somehow before the turn is over, it won’t get the +3/+3 bonus from the Giant Growth because its effect has a limited duration.
  • 502.15h Phased-out cards “remember” their past histories and will return to play in the same state. They “remember” any counters they had on them, any choices made when they first came into play, whether they were flipped when they left play, and whether they were tapped or untapped when they left play. They also “remember” who controlled them when they phased out, although they may phase in under the control of a different player if a control effect with limited duration has expired.
    • Example
      Diseased Vermin reads, in part, “At the beginning of your upkeep, Diseased Vermin deals X damage to target opponent previously dealt damage by it, where X is the number of infection counters on it.” If Diseased Vermin phases out, it “remembers” how many counters it has and also which opponents it has previously damaged. When it phases back in, it will still be able to target those opponents with its upkeep-triggered ability.
  • 502.15i When a permanent phases out, any Auras or Equipment attached to that permanent phase out at the same time. This alternate way of phasing out is known as phasing out “indirectly.” An Aura or Equipment that phased out indirectly won’t phase in by itself, but instead phases in along with the card it’s attached to.
  • 502.15j If an Aura or Equipment phased out directly (rather than phasing out along with the permanent it’s attached to), then it “remembers” the permanent it was attached to and returns to play attached to that permanent. If an Aura phases in and the permanent it was attached to has left play or is no longer legal to enchant, the Aura returns to play and then is placed in its owner’s graveyard. This is a state-based effect; see rule 420. If an Equipment phases in and the permanent it was attached to has left play or is no longer legal to equip, the Equipment returns to play and then stays in play, not equipping anything. This is a state-based effect; see rule 420.
  • 502.15k Permanents that phase in keep the same timestamps (see rules 418.5d and 418.5e) they had when they phased out. This doesn’t change the fact that the permanents phase in simultaneously, however.
  • 502.15m A permanent that phases in can attack and tap to play abilities as though it had haste. This applies even if that permanent phased out and phased back in the turn it came into play. The permanent remains able to attack and tap to play abilities until it changes controllers or leaves play.
  • 502.15n A spell or ability that targets a permanent will resolve normally with respect to that permanent if the permanent phases out and back in before the spell or ability resolves.
  • 502.15p Multiple instances of phasing on the same permanent are redundant.