1) The Flash Races Superman
The all too brief crossover between The Flash and Supergirl wrapped up with a brief race between the Girl of Steel and Scarlet Speedster which was used to send Barry Allen back to his Earth. A rematch wouldn’t go amiss, but The CW could make history by having The Flash find out who the Fastest Man Alive truly is by squaring off with Superman himself.
[zergpaid]That’s something which has happened many times in the comic books (where it’s been established that Barry is definitely faster), but never in live-action. Smallville tried it, but Clark wasn’t wearing a costume and he was squaring off with Impulse, so it’s not exactly the same thing. If the showrunners really want to have some fun, they could throw Supergirl into the mix too, but a race between these heroes would make for the perfect ending to the crossover and ensures it’s something fans talk about for a long time.