"The Silver Key"-Cloud Key

As Cloud Key enters the battlefield, choose
artifact, creature, enchantment, instant, or
sorcery.
Spells you cast of the chosen type cost {1} less
to cast.
There are twists of time and space, of vision and
reality, which only a dreamer can divine; and from
what I know of Carter I think he has merely found
a way to traverse these mazes.