2D art or 3D art? If the former, it looks like some of that is from existing art (e.g., "Bear Rider" is clearly from https://en.wikipedia.org/wiki/Bogatyr#/medi

2D art or 3D art? If the former, it looks like some of that is from existing art (e.g., "Bear Rider" is clearly from https://en.wikipedia.org/wiki/Bogatyr#/media/File:Viktor_Vasnetsov_-_%D0%91%D0%BE%D0%B3%D0%B0%D1%82%D1%8B%D1%80%D0%B8_-_Google_Art_Project.jpg https://en.wikipedia.org/wiki/Bogatyr#/media/File:Viktor_Vas...). The latter is made by the developer, but I wouldn't call those assets "pro quality". This isn't to diminish the astonishing amount of effort that went into the project though!