In initial playtesting we concluded this was powerful, but expensive enough to make it worth it. The wording was (correctly) criticised: I'll try to find a better way to phrase it. I may also add a cost of so this doesn't actually go infinite quite so easily.

So, what methods do you use to playtest your cards?

In the list of details pages above, there's one called "Proxies for printing". I update that page each time I want to do a new playtest, with the decks I want to try, then print them out using the "Printable" link at top-right. They come out 9 to an A4 sheet; I cut them up and slide them inside card sleeves of an already-sleeved deck. Currently all 5 of my sleeved decks are being used as Clockwork Wings proxy decks rather than whatever they were actually assembled as :)

Then I get friends over to my house and recruit them to playtest the decks against each other.

Sometime this summer we're going to have a draft. I think the way I'll do that is print out 3-4 of each common, 2 of each uncommon and 1 of each rare and mythic, then jumble them up into boosters, just of paper. Once people are done drafting they can slide the paper drafted cards into a 40-card deck that's in cardsleeves.

I've also used PyDraft before. Multiverse's plain text spoiler export is deliberately designed to be easy to import into PyDraft.