i like the idea of a decaying card beyond just something that enters the game poisoned. balancing it to be worthwhile may be tricky, though.
I haven't touched this in a while so let's see if my memory still serves correctly.
4
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+ 2
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per turn + 1 card = 4
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+ 3 cards ~= 8
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+ 1 card for 8|4, which at first seems a bit weak, but Clockwork Golem does full damage the first turn for no upkeep, so there is always that.
1
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+ 1
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per turn + 1 card + upgrade = 1
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+ 2 cards +upgrade ~= 3
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+ 1 card + upgrade for 4|4 which is also fine.
The hard part about balancing something like this is fractal or mitosis, but that is also the reason I tried to price it around frog, minor phoenix, and BL.
I can definitely see it being used. It's a compliment to GotP, creates a good
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+
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duo, opens up another good usage of Eternity and RT, and also has synergy with mitosis and fractal.