When playing Ride the Wind, do you have to declare the destination where the unit will move when playing the card, or only on resolution?

Question

Accepted Answer

You must choose the Move destination for the unit when you play Ride The Wind (i.e., as the spell is played), not only on resolution.

When you play Ride The Wind, you choose a valid Destination for the Move at the time the spell is played per the rule for making relevant choices [355] and the specific rule for Moves by spells/abilities [355.4]. The Move instruction will then attempt to resolve to that chosen Destination; if the chosen Destination or other required information becomes illegal or unavailable by resolution, follow the rules for partial or null resolution (e.g., the instruction may be unexecutable) [359.3.e.12] [359.3.e.11].

Play Ride The Wind and, as part of making choices 'as the spell is played', choose a valid Destination for the Move (a Location other than the unit's current Location where that unit is allowed to be present) [355] [355.4] [355.4.a]. Put the spell on the chain/stack and resolve it in turn order. When it resolves, it will attempt to Move the chosen friendly unit to the Destination you selected earlier and Ready it. If the chosen Destination becomes illegal or the unit is no longer in a state where the Move can be executed by resolution, apply the partial/null resolution rules: instructions that can be followed are followed as much as possible; checks against now-illegal objects return null and related calculations are ignored [359.3.e.11] [359.3.e.12]. Ensure the chosen Destination obeys Move restrictions provided by the source and the game (for example, you cannot Move a unit to a Battlefield that already has units from two other players) [444.1] [444.2].

You chose a Battlefield as the Destination when playing Ride The Wind, but before resolution two other players move units there so it now has units from two other players. That Destination is now illegal; the Move instruction cannot be executed to that Battlefield (follow partial/null rules) [444.2] [359.3.e.11]. The unit you chose to Move is removed from the board (banished, returned to hand, killed, etc.) before the spell resolves. The spell's checks about that unit may return null and the Move/Ready may be impossible to perform [359.3.e.12]. You play Ride The Wind during a Showdown. Although Units' inherent Standard Move cannot be done during Showdown [144.1.c], the spell-caused Move is legal because spells/abilities can cause Moves and their legality is governed by the source's restrictions [444.1]. If some effect at play grants an otherwise-invalid Location permission to contain the unit, that Location is a valid Destination per the definition of Valid locations [355.2.b] [355.4.a].

The spell Ride The Wind reads "Move a friendly unit and ready it." Because it is a spell that Moves a Unit, the game requires you to make the relevant choice of the Move Destination at the time the spell is played. Rule 355 instructs that choices for spells are made as the card is played and explicitly says that for Spells and Abilities that Move Units you must choose a valid Location as the Move Destination for each Move that will be performed [355] [355.4]. A valid Location is one other than the unit's current Location where the unit is allowed to be present [355.4.a]. The source of the Move (the spell) provides any additional restrictions on legality for Destinations and global Move restrictions also apply (for example, you cannot Move a Unit to a Battlefield that already has units from two other players) [444.1] [444.2].

Therefore, when you play Ride The Wind you declare where the unit will move at that moment. The spell then goes on the chain/stack and later resolves attempting to Move the unit to the chosen Destination and Ready it. If by the time it resolves the chosen Destination or the unit has changed such that the Move cannot be performed, follow the rules for partial or null resolution — instructions are followed as much as possible and checks against now-illegal objects return null [359.3.e.11] [359.3.e.12].

No further assumptions were necessary; the provided Core Rules contain the relevant guidance.