Bastion Inventor (AER) from Aether Revolt, available at 401 Games Canada.

• Rarity: Common
• Finish: Normal
• Artist: Tony Foti
• Card Text:
  Improvise (Your artifacts can help cast this spell. Each artifact you tap after you're done activating mana abilities pays for 1.)
  Hexproof (This creature can't be the target of spells or abilities your opponent's control.)