Make sure the mpv ipc server is running on /tmp/mpvsocket or edit the script to change the socket.
plplay [<file> | <name> | <url>]
Examples:
plplay song.flac
plplay "select song title (case insensitive)"
plplay part of title
plplay part of file name
plplay "https://www.youtube.com/watch?v=dQw4w9WgXcQ"
plplay "https://www.youtube.com/playlist?list=PLjwyVt8z03-GKz1XgYfF-XhmkQk2Y8GSk"
pladd addonly.flac