Call of Juarez

To kill an enemy using fire you have to throw a lattern and shoot it to make it burst into flames. There are three latterns at the beginning of episode - just turn around when you spawn and you'll see them.

There is indeed 3 lanterns at the beginning. But there's also more through the tunnel (not lit) you don't need to shoot them mid air just throw them at there feet in front, behind, or to the side the fire will spread. Cheevo pops when the third unlucky bastard burns out. :-)