That's right! It's all in the title! You ask a "what if" question about the Shafferbots VS. Wieserbots universe, and that becomes the basis for an RP in a timeline separate to the main one!
"Portal" -- Shafferbot #1 has built an interuniversal portal generator in his basement labs. You describe what comes out of it. Lots of crossover opportunities here.
"Conglomerate Universe" -- Two or more universes are combined.