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Your attitude towards the situation is rather dismissive of the amount of work that has gone into the game as a whole, and it ignores the fact that the reused assets in the game have been edited and transformed into something new entirely. It's not uncommon to see artists using existing art as inspiration for their own, which is what I see happening here. While there are some similarities between the original art, and the edited art in Cursedom, it has still been edited to the point that the differences outweigh those similarities, which, in my opinion, makes it justifiable to ask for donations in this scenario. This holds especially true when you think about the amount of work put into the game on the whole, even if they removed the art you pointed out, there is still an entire game there that took a lot of work to create. To close off any form of funding entirely just because of some assets that are based off existing art, would be absurd and dismissive of the rest of the work put into this game.

I think in the end, it boils down to "If you have an issue with the game, don't pay for it." The game is offered to you entirely free, and only costs money if you want to support the developers. If you don't want to support the actions made by the devs, then don't. Obviously it's not something that bothers everyone, since some people have donated money, but if it bothers you, then don't pay.