From the gatherer
Citation :
The value of X needs to be determined both when the ability triggers (so you can choose a target) and again when the ability resolves (to check if that target is still legal). If the number of Faeries you control has decreased enough in that time to make the target illegal, Spellstutter Sprite's ability will be countered (and the targeted spell will resolve as normal).
Ca check aussi le nombre de faerie au moment où la capacité se résout.
Quand elle se résoudra il aura quand même un peuple fée en jeu (
Farfadette cafouillesort)
Donc x=1 et le gobelin sera quand même contracarré