Vial of Stardust

This enters the battlefield taped and does not untapped during your upkeep unless this has a time counter on it. {p/c}: discard 2 cards. Put a time counter on this artifact.
{t}:prevent all combat damage until this untaps. When this untaps do to your upkeep, chose 1:
-Remove a time counter and give this card: At the beginning of your main phase, discard a card. If you can not, sacrifice this artifact, until it leaves the battlefield.
- Put this card on the bottom of your library.