Accelerondo (Accelerando in the Japanese version) is a battle theme in Mother 3. As the name would imply, this song grows gradually faster, making it one of the most dynamic songs in the game. The song consists of snare drum, timpani, and strings.
Stringent (sometimes known as Stringendo) is the alternate version. It's basically the same, except that it's slower all around and uses a diminished version of the Accelerondo chords.