Zack Snyder's Justice League: Everything we know so far

The film would have explored Flash's time travel powers

Remember that weird scene from Batman V Superman where Flash travels back in time to warn Batman about future events with no explanation?, well as it turns out Snyder's version of Justice League was supposed to provide context to that scene by exploring Flash's ability to time travel through the speed force, as Flash was supposed to learn how to time travel for the first time in the climax of Snyder's cut of Justice League where after Superman and Cyborg fail to stop Steppenwolf from using the Motherboxes to form the unity, Barry would have gone back in time to a few seconds earlier and prevented Steppenwolf's victory. as you can tell, The Flash was meant to have a much bigger role in the Snyder cut of Justice League compared to the theatrical version which cut out all the time travel elements. not only that, but Barry's love interest Iris West was supposed to make an appearance early on in the movie played by actress Keirsey Clemons in a scene where Barry would have saved her from a car accident, the scene intended to be a showcase of Barry's super speed. it is unknown why her character was cut from the theatrical version of the movie, but she was meant to be a crucial piece of Barry Allen's character development in the Snyder cut. there was also supposed to be more emphasis on the relationship between Flash and Batman, as Ezra Miller described his role in Justice League as "a fanboy meeting his heroes for the first time", showing the young recruit's admiration for these larger-than-life heroes. though Barry's admiration for the caped crusader is still present in the theatrical version, the Snyder cut would have further developed their relationship and explored more of Batman's development into a mentor figure for the scarlet speedster in a similar manner to how the relationship between Tony Stark and Peter Parker was explored in the MCU. not only that, but Flash's friendship with Cyborg was also meant to be more fleshed out in the Snyder cut forming a tight brotherly bond over the course of the film, which would have led to Cyborg himself making a cameo in the still-stuck-in-development-hell Flash solo movie. speaking of Cyborg...