Mastery Of Mana

Mastery of mana enters the battlefield with X
mana counters on it.
At the beginning of your upkeep, put one
mana counter on mastery of mana.
At the beginning of combat on your turn, you
may cast a creature spell with converted
mana cost X or less without paying its mana
cost, where X is the number of mana counters
on mastery of mana.