Mocking Sprite

Creature — Faerie Rogue

Flying

Instant and sorcery spells you cast cost less to cast.

Mocking Sprite's last ability doesn't change the mana cost or mana value of any spell. It changes only the total cost you pay.
Mocking Sprite's last ability can't reduce the amount of colored mana you pay for a spell. It reduces only the generic mana component of that cost.