Trap Filled Corrodor

{1}, {t}: Look at the top four cards of your library.
You may exile one card face-down, and put the
rest on the bottom of your library in any order.
Do this once when Trap Filled Corridor enters
the Battlefield.
{1}{t}: You may cast one Instant or Sorcery exiled
with Deadly Tomb as if it had Flash. The mana
cost is reduced by {4} and you can use any any
color mana to do so. Activate this ability only
during an opponent's combat phase; and only if
they attack.