The event shop uses the event currency, which is Crystal shards. You get them by posting and battling, and you can see how many you have beside your avatar at the top.
Uni has swallowed me whole, in more ways than one, sorry guys. Feel free to PM any questions (or nonquestions {or anything else, no limits here}) you have, although I don't know when I'll get to them since I'm barely on atm.
Regarding the topic though, I'm glad you brought this up. I'll definitely ask Cat about adding something to those shops telling users what to pay with if she doesn't see this topic herself!.
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