Last Boss Remix is a song from Silent Hill 3, released on the Silent Hill Sounds Box. It is track 8 and was composed by Akira Yamaoka. It is the final boss music from Silent Hill 3. The name of this track is quite misleading, as it is not a remix of any kind.
This track is also featured in the Silent Hill film, playing when Alessa Gillespie appears in the church and begins her revenge on Christabella and the Brethren. Additionally, it features a new organ at the beginning before playing the proper melody. (This version can be heard here.)