355.12. If a spell specifies that a player may perform a Game Action on some number of Game Objects, then all choices are considered targeted and chosen independently of the decision to perform the Game Action.
355.13. 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.
355.15. These choices cannot be changed after this step unless instructed to by a spell or ability. See rule 750. Making New Choices for more information.
355.16. 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 a card which reads "As an additional cost to play this, kill the unit you control with the most Might. Give a friendly unit +[M] equal to the killed unit's Might this turn. Predict 2." They cannot choose to target their unit with the highest Might during this step of finalization.
355.17. If a spell or ability requires one or more players to make choices that are not outlined in this section, they are made on resolution.