The sap that falls for this won't have a good day. The card's info says:
RB09-EN030:
Cruel Pranks
Normal Spell
When you control "Gilda, Griffon of Ponyville": Activate 1 of these effects.
- Return all monsters your opponent controls to the Deck, and if you do, Set cards in your opponent's Graveyard to their side of the field equal to the
number of cards you returned to the Deck. (Treat Spell/Trap Cards Set this way as Normal Monster Cards (Level 1/ATK 0/DEF 0).
- Set as many cards in your hand as possible from your hand into your Spell and Trap Card Zones, and if you do, destroy cards your opponent
controls up to the number of cards you Set from your hand this way.
Rainbow Rare