I was thinking about Power Grid promo yesterday, don't have a card ready, but I think the idea is far enough to post it here, maybe someone will fill the holes better than I can
So I wanted to start with electricity. The only medieval "source" of electricity is a lightning. Then power plant #50 came to my mind (
http://cf.geekdo-images.com/images/pic135555_lg.jpg - at the bottom), as everyone I play Power Grid with says this one is powered by lightnings closed in the glass ball. So this should not be an ordinary lightning. Ball lightning is definitely more cool. And the cool thing I would like to do with a ball lightning is throwing it at my opponents.
And the card of course has to be Victory card as well, to be at least partially green
Working off cards you trashed - the more your lightnings burn, the more victorious you are.
So what I have right now is:
Ball LightningAction-Attack-Victory
(some attack here, maybe some small bonus as well if the attack isn't too strong to allow this)
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Worth 1 VP for each 5 cards on your trash card (rounded down).
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In games using this, each player uses his own trash card to store cards he trashes.
The set would come as 19 cards: 12 standard, 1 randomizer, 6 alternate art trash cards. Or maybe 6 trash mats - so that the Dominion time machine works at least a bit
What I'm most unsure about is the attack text. It definitely should be a trashing attack. A lightning is something that could take two objects and melt them into one - so I thought about something like a forced Forge, where your opponent doesn't have full control about what he receives. But is should not decrease the deck size (as this could lead to people ending up with too small decks to do anything). I tried to invent something good but so far couldn't, so I decided to post it, maybe someone has a good idea for attack for this card