When attacking with 2 Anivia into a battlefield with 2 Nocturnes and a hidden Teemo Strategist, when is the latest the defending player can flip Teemo before losing control of the battlefield due to all units dying to Anivia triggers?

Question

Accepted Answer

The defender must flip (play from Hidden) Teemo - Strategist as a Reaction in response to the Anivia trigger that would kill the last defending unit(s). The latest safe moment is on the chain in response to that lethal trigger (i.e., before that trigger resolves); doing so puts an item on the chain and prevents loss of control so you can play Teemo - Strategist to that battlefield. If you wait until after the lethal trigger has fully resolved and there are no items on the chain (cleanup), you will have lost control and cannot play it there. [811] [FAQ:unleashed#16]

Play Teemo - Strategist from Hidden as a Reaction to the Anivia trigger that would kill the final defending unit(s). The play must be initiated before that lethal trigger resolves (or while there is still an item on the chain created by some pending effect). If no item remains on the chain and cleanup completes (you lose control of the battlefield), you are too late and cannot play Teemo - Strategist to that battlefield. [811] [FAQ:unleashed#16]

Attacker's Anivia attack and any associated triggered abilities are placed on the chain (the lethal effects that will kill defending units are pending). [359] [355] Before the lethal trigger(s) resolve, the defender may play Teemo - Strategist from Hidden as a Reaction (Hidden grants Reaction while facedown and when played from facedown). This play must be to the battlefield where it was hidden. [811] [355] Because playing Teemo - Strategist from Hidden opens a chain item (it is being played), there is an item on the chain while the play finalizes; presence of an item on the chain prevents immediate loss of control during the subsequent cleanup, so you can finalize the play and have Teemo - Strategist enter that battlefield. [811] [FAQ:unleashed#16] If the defender waits until after all lethal triggers fully resolve and cleanup finishes (and no items remain on the chain), control is lost and the defender can no longer legally play Teemo - Strategist to that battlefield. [FAQ:unleashed#16] [811]

If the particular Anivia interaction never puts a chainable item on the chain (for example, if damage and deaths are all resolved without any triggered abilities being placed on the chain), the defender's only safe window is before resolution/cleanup — they must flip before the resolution that kills the last unit and before cleanup. [811] [359] If some other effect on the chain already prevents losing control (e.g., another pending spell or ability), the defender could wait longer and still flip while control is retained. The general rule is: flip any time there is still control of the battlefield or while an item on the chain prevents cleanup removal of control. [FAQ:unleashed#16] If flipping/playing Teemo - Strategist as it resolves requires choosing targets or affects other locations, note play-from-Hidden restrictions: a hidden permanent must be played to the battlefield where it was hidden and play-time choices that target must be chosen from that battlefield unless the card's text makes that impossible. [811] [355]

Short answer: flip Teemo - Strategist in response to the Anivia lethal trigger (i.e., before that trigger resolves). Why: A Hidden card gains Reaction and may be played from facedown as a Reaction; playing it opens a chain item and must be played to the battlefield where it was hidden [811]. If you play Teemo - Strategist as a Reaction to the lethal Anivia trigger, the resulting pending chain item prevents the game from performing cleanup that would cause you to lose control of that battlefield, so you can legally have Teemo - Strategist enter that battlefield as it finalizes [FAQ:unleashed#16]. If you wait until after the lethal effects fully resolve and cleanup completes (and nothing else is on the chain to prevent losing control), you will have lost control of the battlefield and can no longer play the Hidden card there because Hidden requires you to play the permanent to the battlefield where it was hidden, which you no longer control [811].

Because the exact texts/timing of the involved Anivia and Nocturne cards weren't provided, this ruling assumes the lethal effects are chainable triggers or otherwise create a reaction window you can use. If some other pending item on the chain already prevents loss of control, you can wait until that item resolves; in all cases you must flip/play Teemo - Strategist while you still control the battlefield (or while a chain item prevents cleanup), otherwise the play is illegal. [355] [359] [421] [811] [FAQ:unleashed#16]