Bolas's Citadel

Bolas's Citadel
{3}{B}{B}{B}

Legendary Artifact (CMC 6)
You may look at the top card of your library any time.
You may play lands and cast spells from the top of your library. If you cast a spell this way, pay life equal to its converted mana cost rather than pay its mana cost.
{T}, Sacrifice ten nonland permanents: Each opponent loses 10 life.