Ashnod's Altar by sacrificing another creature, adding ({C} magic symbol) ({C} magic symbol) .
When the creature dies,
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Extractor Demon triggers, causing you to mill two cards if your graveyard is empty, or causing an opponent to mill two cards otherwise.
If your library is empty, activate
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Soldevi Digger by paying ({2} magic symbol) , putting a card from your graveyard onto the bottom of your library.
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Quintorius triggers, creating a 3/2 Spirit creature token.
Repeat.
Notes
The combo will grant you an amount of ({C} magic symbol) equal to the number of cards in your library, as you do not need to do step 3 as long as your library has cards in it. You can instead also target an opponent in step 2 if your graveyard is not empty.