Cannot be Normal Summoned or Set. Must first be Ritual Summoned. You can Ritual Summon this card with any "Gishki" Ritual Spell Card. When this card is Ritual Summoned: Target up to 5 cards in any Graveyard(s); shuffle those targets to the Deck.
Gishki Aquamirror is currently the best Ritual Spell card for Gishki ritual monsters. It can recycle itself from the Graveyard to your Deck, at the same time you can also recycle 1 Ritual monster from the Graveyard back to your Hand as well. Forbidden Arts of the Gishki is a powerful Ritual Spell card to use your opponent’s monsters as tributes for your Ritual Summoning instead, but the drawback is your Ritual Monster’s ATK is halved and you cannot conduct Battle Phase during the same turn.
Gishki Ariel has Flip effects that searches for any “Gishki” monsters from your Deck to your Hand, this includes Evigishki Mind Augus. Gishki Natalia has effects that target 1 “Gishki” monster in your Graveyard and return it to your top Deck, this includes Evigishki Mind Augus. Aquamirror Meditation can return 2 “Gishki” monsters from the Graveyard to your hand, this includes Evigishki Mind Augus.
As all Gishki monsters are WATER attribute, those level 5 or higher Ritual monsters can benefit from Sea Stealth Attack effects. This greatly enhance their combat ability to play around cards like Wall of Disruption since Gishki decks generally lack the cards to deal with opponent’s backrow. You can use Moray of Greed to shuffle 2 WATER monsters from your hand to your Deck and draw 3 cards.
This boi is so strong against REZD, magnets, CA maybe. It can get rid of beacon savers, machine angel ritual or Red Eyes Zombie dragon from the graveyards. I don't know if red eyes spirit is chainable to this effect but even so, its 2500 ATK is enough to get over it.
You could possibly build a deck with this and the other level 6 gishki ritual (tetrogre). You can play sea stealth attack with this thing and ritual weapon too (even if it may be a bit useless). Tetrogre, instead works like a foolish burial except it can also become a -1 for your opponent if he decides to do so. You can send to the graveyard beacon saver (which works well with lv6 rituals because it is lv2), A/D changer, Skill successor or even gishki aquamirror to get a free search.
I think many underestimate gishkis but they have a lot of potential.