10) Reverse-Flash
The first time we heard Rip Hunter’s name was when Eobard Thawne mentioned him in The Flash. While it was little more than a throwaway line, there’s clearly some history there, and delving into that has a lot of potential (even if it’s just for a single episode).
While we still don’t know how the events of “Flashpoint” will impact the DC TV Universe, it was revealed in season two of the Scarlet Speedster’s series that a time remnant of Thawne exists, so the team crossing paths with him in Legends of Tomorrow could work without further complicating the timeline.
The Reverse-Flash loves to travel through time causing chaos, and with Hunter now essentially the last Time Master, some sort of confrontation with this villain feels like an inevitability during season 2.