Whir of Invention [Aether Revolt Promos]

Set:	Aether Revolt Promos
Type:	Instant
Rarity:	Rare
Cost:	{X}{U}{U}{U}

Improvise (Your artifacts can help cast this spell. Each artifact you tap after you're done activating mana abilities pays for {1}.)
Search your library for an artifact card with mana value X or less, put it onto the battlefield, then shuffle.