The Yellow Sign

The Yellow Sign enters the battlefield tapped.
{t}: Add {u}, {b}, or {r}.
{x}{u/b}{b}{b/r}, {t}, Sacrifice The Yellow Sign: Each
opponent reveals the bottom card of their library.
You may cast a spell revealed this way with mana
value X or less without paying its mana cost.
"Have you seen The Yellow Sign?"—R.W.Chambers