Skeletal Swarming (AFR) from Adventures in the Forgotten Realms, available at 401 Games Canada.

• Rarity: Rare
• Finish: Normal
• Artist: Svetlin Velinov
• Card Text:
  Each Skeleton you control has trample, attacks each combat if able, and gets +X/+0 where X is the number of other Skeletons you control.
  At the beginning of your end step, create a tapped 1/1 black Skeleton creature token. If a creature died this turn, create two of those tokens instead.