Necromancer's Guile

Necromancer's Guile enters the battlefield with
X tomb counters on it.
You may cast cards from your opponent's
graveyard and you may spend mana as though
it were mana of any color to cast those spells.
At the beginning of your upkeep, remove a
tomb counter from Necromancer's Guile. When
Necromancer's Guile has no tomb counters on it, sacrifice it.