Re: Beneath the Comet
I wasn't sure if you were using the Rivals or not. Since you are, I would max out their numbers and maybe give them some henchmen. Also, you could play them a little smarter than you would if there were fewer PCs. Make full use of aerial reconnaissance, flying spell casters, punji stick pits with poison, etc. There is one "trick" by the Rivals included in the adventure, but there's no reason you couldn't add more along the same lines. Just try to gauge how many your players are likely to fall for.
"The fear of death, its risk each time, is one of the most stimulating parts of the game. It therefore behooves the referee to include as many mystifying and dangerous areas as is consistent with a reasonable chance for survival." - J. Eric Holmes