Use this card's effect, then Ritual Summon "Evigishki Mind Augus" to return the card your opponent sent.
This card makes an excellent combo with "Gishki Aquamirror". You can send the "Mirror" to the Graveyard each turn, then activate its effect and return a "Gishki" Monster from your Graveyard to your hand by returning "Gishki Aquamirror" to the Deck, all the while forcing your opponent to eliminate their own Spell Cards. Even if your opponent stops the effect by choosing to discard a card, you're still gaining hand advantage.
After you Ritual Summon this with "Gishki Aquamirror", send a "Gishki" Ritual Monster to the Graveyard in order to add it to your hand with the effect of "Gishki Aquamirror".