Noxious Trap

You may cast this card from your sideboard by
paying {2} rather than pay it's mana cost as long
as your library has twenty or fewer cards in it.
Put a -0/-1 counter on target creature, then tap
it. At beginning of the next end step, return
Noxious Trap from your graveyard to your
sideboard.
"Armed and ready."
-Teemo, the Swift Scout