2) Power Girl
Season one ended on a cliffhanger, as a pod similar to Kara’s crashes into Earth. We don’t see who it is, but Kara’s shocked face tells us it is someone pretty important.
There are lots of theories going around the internet right now, but the most popular is that the pod contains Power Girl, a version of Kara from a different universe.
After the Flash’s arrival introduced the idea of alternate worlds to the show it wouldn’t be too much of a leap for this to happen. It does make sense if they’re trying to do something that will improve the show for its second season: two Supergirls are better than one, after all.
Power Girl is usually more of a wilder, outgoing sort than Supergirl, so her introduction could make for a lot of fun as Kara comes to terms with this very different version of herself.