When news of the fake app spread online this morning, StudioMDHR took to Twitter to confirm that this is not a real version of Cuphead and it will be working to contact Apple and remove the app as soon as possible.
There is a Cuphead imposter app on the iOS store -- this is a scam. We are working on removing the fraudulent app ASAP!— Studio MDHR (@StudioMDHR) December 18, 2017
Apple's app review process tends to be very strict, so it's again unclear how a fake app asking users for money made it past the company in the first place. For MyEtherWallet, that fraudulent app also charged people $4.99, making it as high as #3 on the App Store's Finance charts and existing on the store for over one week. Apple eventually removed the app from the App Store, which it is expected to do for Cuphead as well.
Update 7:32 a.m. PST: Apple has removed Cuphead from the iOS App Store.