Star Wars Universe vs. Star Trek Universe
Some manner of godly trickery has placed the two respective universes in striking distances of each other, by way of some manner of celestial tech. The various factions in each have united (Sith, Jedi, Rebellion, Empire etc as one and Borg, Federation, Klingons etc. as one) and are now raging an intergalactic war the likes of which have never been seen. The prize is survival and domination or the looser...
So which universe takes it? Who is the force really with? Is it possible for the factions to work together well enough to win? Does Star Trek live long and Prosper? Or does Star Wars reveal the true power of the dark side?
There are no rules, any weapons, skills, troops or tech normally possessed by the two respective universes can be utilised.