Hourglass of Fate

Hexproof
Hourglass of Fate enters the battlefield with {x} time counters on it.
so long as Hourglass of Fate has a time counter on it, it's controller cannot lose the game.
when the owner of Hourglass of Fate is attacked, prevent all damage and
remove time counters equal to the damage prevented.
if Hourglass of Fate reaches zero time counters, it's controller loses the game
{x}{t} add {x} time counters onto Hourglass of Fate