Time Keeper

As long as you control Time Keeper, whenever
an opponent casts a spell you may pay that spells
mana cost, if you do then negate it's effects and
return it to it's owners hand. {u} can be used as
any color mana for this effect.
If "Time Keeper" would be destroyed, instead
exile it. You may play it at any time from exile
for its mana coast +{x} where X is twice the
number of times you have played it.
You may only have one Time Keeper in your
library.