Cloud Key
Artifact
As Cloud Key enters the battlefield, choose artifact, creature, enchantment, instant, or sorcery.
Spells you cast of the chosen type cost 
less to cast.
"A key only unlocks a door. Its wielder must choose whether to cross the threshold." —*Hurkyl's Metaphysics, vol. II*
Illustrated by
The Brothers' War Retro Artifacts#75zRareEnglish