While mana is sometimes directly converted into cards, by way of plays like Divination (which converts three mana and a card into two cards), more commonly, mana is traded for influence over card quality
This way you can play the card even if youre tapped out, allowing you to play multiple spells on a turn or play a spell after tapping out for the ninjutsu cost
Only 4 of these cards have ever been confirmed to exist, making it one of the most sought-after cards of all time
For example, Kaheera, the Orphanguard's restriction is that all creatures in the deck must be either a Cat, Elemental, Nightmare, Dinosaur, or Beast card
Any card that ramps for two and costs two is a big deal and with little effort Priest is about that