Two interesting things about this card:
- It triggers whenever one of your creatures attacks and not whenever it "deals combat damage to a player." So you're guaranteed the extra mana as soon as you commit to combat.
- It stores the mana as charge counters until the charges are used up.
I imagine that the idea for this card came up long after it was decided that Innistrad was going to be a token heavy set. Gather the Townsfolk, Midnight Haunting, and Druid's Repository deck that ramps into any number of potential angels & demons? Or let's go even bigger and start talking X spells like Devil's Play and Increasing Confusion. How crazy would that be?