There is a very long thread with many examples of the Fuse license. You are allowed to use Fuse figures in your game or video – your creative projects. You are not allowed to asset-flip: sell or give away game-ready figures made with Fuse content for others to use in their projects.
Mixamo is in fact a sub-product of Fuse and shares the same terms
p,s. no you don't need to give credit
Digital characters, like people, have similarities and differences so when you build digital characters, they are unique unless you buy characters that someone else built. You write something and copyright it. It's yours. Somebody else writes something it;s their's. Some sites sell the use of digital characters that they built. Some sites sell the opportunity to build them yourself.
That's how I understand it.
Have a great day.