Fen Hauler (AER) from Aether Revolt, available at 401 Games Canada.

• Rarity: Common
• Finish: Normal
• Artist: Sidharth Chaturvedi
• Card Text:
  Improvise (Your artifacts help cast this spell. Each artifact you tap after you're done activating mana abilities pays for 1.)
  Fen Hauler can't be blocked by artifact creatures.