This is an asymmetrical card that prevents spells from being cast by your opponents unless those spells were cast from their hands
Being able to put any number of creature cards onto the battlefield when this card enters is an absurd boon, especially if you can cheat it into play with a reanimation spell
Midnight Clock As noted in the Honorable Mentions, we've left some very popular mana rocks out of this ranking on grounds of them being cantrips rather than providing card advantage
Twin primes are pairs of prime numbers that differ by only two, such as 3 and 5, 5 and 7, 11 and 13, and 17 and 19
While that never came to pass, its a solid 3-mana counter
Tokens: she puts three creatures on the board, something Mentor of the Meek greatly appreciates