Bolas's Citadel

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
mana value rather than pay its mana cost.
{t}, Sacrifice ten nonland permanents:
Each opponent loses 10 life.
"End, begin, all the same. Big change. Sometimes good. Sometimes bad."
—Aughra, The Dark Crystal