This is the most common point of frustration regarding the Mugen Archive login. You have successfully logged in, you search for a character, you click the download button, and... nothing. Or an error message saying you do not have permission.
Locate the "Register" button in the top right corner. mugen archive login
The official domain has changed over the years due to hosting issues. As of this writing, the primary domain is (always check for the https:// prefix). Avoid fake clone sites that try to steal login credentials. This is the most common point of frustration