352.1. If the card is a spell, or has an effect that specifies a choice "As I am played," those choices are made now.
352.2. For Units , choose a valid Location where that Unit will be placed upon being Played.
352.3. For Spells and Abilities that Move one or more Units , choose a valid Location as the Move Destination for each Move that will be performed.
352.4. If a card requires you to specifically choose one or more Game Objects , that choice is made now.
352.6. When a card Chooses one or more specific Game Objects to affect, it is Targeted.
352.7. In order to put a spell or ability on the chain, valid choices must be made for all targets.
352.8. A target is a valid choice if it meets all of the following requirements:
352.9. If a spell or ability requires one or more players to choose objects, players, or zones that are not targets, those choices are made on resolution.
352.10. A game object, player, or zone mentioned in the text of a spell, activated ability, or triggered ability is a target UNLESS any of the following are true:
352.11. Some cards identify a group of Targets with Targeting Requirements that must be met by the group as a whole.
352.12. If a card specifies that a player may choose some number of Game Objects to be affected by a card, then all choices are considered targeted and chosen independently.
352.13. If a card specifies that a player chooses “any number” or “up to” some number of Game Objects to be affected, they may choose any number of available targets, including zero. If they choose zero, the spell or ability can be played without any targets.
352.14. Splitting
352.15. These choices cannot be changed after this step.
352.16. A player may not make choices during this step that will deterministically result in illegal choices or actions later in this process unless they have no choice. Example: A player plays Cruel Patron, which says "As an additional cost to play me, kill a friendly unit." They control exactly one unit, which is at a battlefield. They can't choose to play Cruel Patron to that battlefield, because by the time they have finished paying costs, they will no longer control that battlefield.