Here is a second clip from Monday's new episode of Supergirl called Medusa. Here we see Cyborg Superman planting a device in the alien bar while Mon-El follows him out, thinking it's J'onn J'onzz. The two fight briefly in the alley while the device starts kicking out a gas into the bar, taking some patrons down while cause the rest to run.
This is the first part of the 4-series Invasion crossover, but it looks like there will be quite a bit of stuff going on before the Flash shows up to invite Supergirl back to his Earth.
Supergirl airs Mondays at 8 PM on the CW.