It is never legal to sell something that is a licensed/copyrighted character. Even if you rename it or change it slightly. Even giving it away for free has risk involved, albeit less risk than if you were to charge. The only exception is ‘public domain’ characters. See the link above for a decent discussion, though the list of public domain characters is out of date. For instance, steamboat willey I believe became public domain (or was it moritmer mouse?) and so did winney the pooh. Hence why they made horror movies of those recently. But you’re always taking a risk unless you get special permission. And I guaranty you’ll have a rough time getting special permission from Nintendo, Disney, Pixar, etc. The big names will charge a lot. I know someone said they paid 2k just to sell at a disney event for disney characters and they had to get preapproval for everything they were selling.
