cr:1.8.3b

If any of the optional effects cannot be generated due to a rule or effect, cannot resolve successfully based on the current game state, or contain an asset-cost which cannot be paid,[1.14.2] the effect cannot be generated/applied and the player cannot choose to generate/apply the effect. If the optional effects are phrased with “may choose to” then the player may choose to generate the effects regardless of their outcome.

Example: Murky Water has the text “. . . you may banish face-down 3 traps from your graveyard.” If the player 3 or more traps in their graveyard, they may choose whether or not to generate the effect to banish them. If they have 2 or fewer traps in their graveyard, they have no choice and the effect is not generated.

Example: Heave partially means “. . . you may pay {r}{r}{r} and put this face-up into your arsenal.” If the player cannot pay the resource cost or they cannot put the card into their arsenal, they cannot choose to heave the card. The player must both pay the asset-cost and be able to put the card into their arsenal to be able to heave the card.

Example: Mark of the Huntsman has the text “When this hits a hero, you may choose to destroy this and mark them.” Even if Mark of the Huntsman cannot be destroyed or the hero is already marked, the player may choose to generate the optional effects, in which case Mark of the Huntsman will be destroyed (if able) and the hero will be marked (if able).