Boomstacker (UND) from Unsanctioned, available at 401 Games Canada.

• Rarity: Rare
• Finish: Normal
• Artist: Jesper Ejsing
• Card Text:
  As Boomstacker enters the battlefield and whenever it attacks, stack two dice on top of it. (All dice must be stacked vertically, one on top of another.)
  Boomstacker gets +1/+1 for each die in its stack.
  Boomstacker attacks each combat if able.
  When the stack falls, sacrifice Boomstacker.