To convert a Super Mario .wav file into a ringtone, click on the .wav files and drag them into iTunes. Once the files appear on the Music tab, press "Ctrl" then "L" or right-click one of the files and select "Get Info," then click the "Options" tab. Replace the "Start" and "Stop" times to the part of the song you want as your ringtone and click "OK." Skip this step if the .wav file is already at the desired length.
Back on the iTunes window, right-click the modified file and choose "Create AAC version." This makes a converted AAC copy of the file. Right-click the new file in the iTunes window and select "Show in Windows Explorer" to open the file folder. On "Windows Explorer," click the "View" tab and check "File Name Extensions." Doing this makes the file's extension appear, which should read .m4a. Rename the file by clicking on it once and replacing the extension from "m4a" to "m4r," then press "Enter" to save the changes. If the operating system asks you if you are sure about changing the file extension, click "Yes."
After renaming the file, drag the new file back into iTunes and add it to the library as an iPhone ringtone. You can now delete the .wav and .m4a files from your library. You may also re-check the "File Name Extensions" box back on the "Windows Explorer" folder to re-hide the extensions.