Rule · Chapter 1
cr:1.8.9
An effect fails if (A) it is a targeted effect and all declared target(s) are no longer legal or have ceased to exist, (B) the effect requires additional parameters and there are no legal parameters that can be chosen, or (C) if all the events it creates fail to occur. If there are sufficient parameters to allow the effect to be generated and at least one event that it creates does not fail to occur, the effect does not fail.
Example: Flick Knives has the text “Target dagger you control that isn’t on the active chain link deals 1 damage to target hero.” If the dagger that is targeted ceases to exist before the effect is generated, the effect fails to be and no damage will be dealt.