And El Mariachi is a battle theme in Mother 3. Despite the name, the song is actually a tango, which is quite easy to combo to. 2/3 into the song, it becomes a bossa nova, almost like a background song at an elevator. You can also hear this song when fighting an unused boss called Straw.
And Yet, El Mariachi
And Yet, El Mariachi is the harder version. It is basically the same, except that at 2 times, the player must follow the three notes that play in slow succession. These happen at 0:28 and 1:10. It also slows down very slightly at 0:11.