This card's effect that adds a Spell from your Deck to your hand is the effect that is applied by activating this card. (It cannot be activated during the Damage Step.)[1]
This effect targets 1 Spell in either your GY or your opponent's GY. (You must target a Spell with the same name as a card in your Deck.)[1]
This card's effect that Special Summons a "Witchcrafter" monster from your Deck starts a Chain and activates in the GY. (It does not target, and cannot be activated during the Damage Step.)[1]
Banishing this card and 1 or more Spells from your GY is the cost to activate this effect. (The number of Spells you banish must be equal to the Level of a "Witchcrafter" monster in your Deck.)[1]
A: As in this scenario, if the Spell targeted by the effect of "Witchcrafter Masterpiece" is no longer in the GY when the effect resolves, the effect cannot be applied.[2][3]