battle legion booster box S9a Shield Era The Battle Cards section has

Agido and Kelbek (the "millers") can send multiple cards from both players' decks to the GY, while Keldo and Mudora (the "shufflers") can recycle cards from the GY back into either players' decks

So that deck sticks out as the unique one in the bunch

It should at least see some play in aggressive black decks, and in this regard, its similar to cards like Okiba Reckoner Raid

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As such, even an effect as simple as Grave Pact works wonders in conjunction with Sephiroth