Updates to Left 4 Dead 2 have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:

Left 4 Dead 2
  • Encore Mutation: Follow The Liter
  • Added support custom campaign particles. Custom campaigns can specify their own particles_manifest.txt file as well as any per map files. The per map files need to reside in the maps directory and be in the form: <mapname>_particles.txt