Some real long time ago, in the Future Sight set, there was an ability that allowed us to spend much less mana to cast certain spells in a late game when the graveyard was full of cards
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First, look at the rarity symbols on your cards: a circle indicates a common card, a square represents an uncommon card, and a star denotes a rare card
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Using the Mardu mana combination of red, black, and white, this deck focuses heavily on bringing cards back from your graveyard for a second chance at doing damage to your opponents, and the Commander even mills two cards every turn to try and put some spicy creatures in there for them to bring to the battlefield later in your turn