If you Ritual Summon exactly 1 WATER Ritual Monster with a card effect that requires use of monsters, this card can be used as the entire requirement. You can discard this card; add 1 "Gishki" Ritual Spell Card from your Deck to your hand.
First effect can only be used when summoning WATER Ritual monsters.
Gishki Ritual Spell
Here are the cards you can search with Gishki Shadow’s effect. Forbidden Arts of the Gishki is a great removal card while also summoning a weakened Gishki Ritual monster. Gishki Photomirror lets you Ritual Summon even without tribute fodder.