The theme for CharCon (charcon.org) this year was monsters vs. aliens, so I expanded it a bit and ran a "Cowboys vs Monsters vs Aliens" event. The game had six players, and used the gold rush scenario. As the gangs explored the town. Terrain was somewhat interactive. As gangs explored the table they might find that the train could be driven or locals that would join their team.
Cowboys:
Los Banditos Mexicanos
Custom Gang made from clix minis
Monsters:
Croatan's pack (cards from website, proxy miniatures)
Custom Savage Beasts gang (mix of prepaint/board game minis)
Aliens:
Two gangs of Alien Invaders from Brigade Games.
I used the cowboy gangs as the basis for the aliens, adjusted the stat maximums +1 Int/-1
Str. The weapons used normal stats, but added an ability and raised the level by 1. I also gave them some various other abilities to support the theme.
Notes from the game:
Croatan's pack had a hard time. Any time one of them left a building, they died. Not having ranged attacks is a huge penalty, and I don't think the free skill quite makes up for it.
Anyway, here are a few pictures. It was great fun.