itch.io

if these assets are completely from nintendo design, you can not really put a license, but if these are inspired and are unique to you, you can check the creative commons license versions. 
Which includes for example these;

https://creativecommons.org/cc-licenses/

there is also CC0 which means you don't hold any rights (for example, someone can come and download these assets, and sell as it is, this much permissive).

If the license versions on the CC-BY and etc seems no to you and CC0 is too permissive, you can just include a basic text in this page, such as:
- (If you allow non-commercial and commercial)
- (If you want credit or not, if you do not want credit, you can also say that credit is appreciated)
- (If these models are allowed to be used in NFTs, in AI-training stuff, which I guess no (generally everyone writes no))
and that's it for about what I know.