Justice League: Gods and Monsters Chronicles, on Machinima (YouTube)
DC Database; IMDb; TV Tropes; Wikipedia

This is a three-episode (each about 6 minutes) animated series that was released in June 2015, leading up to the July 2015 release of the movie Justice League: Gods and Monsters. It was originally released on Machinima's YouTube channel, but it was gone by the time I watched the series in January 2022, so I watched it on a different YouTube channel (which I'll link to below). Hopefully the webisodes will stick around, there. Apparently there was supposed to be a second season of webisodes in 2016, but that never materialized. The series, like the movie, is much darker than the usual animated DC fare.

Twisted
This episode features Batman (apparently not Bruce Wayne) battling a deranged Harley Quinn. In the end Batman is revealed to be a vampire.

Bomb
Brainiac is destroying Metropolis, and Superman is nowhere to be found. So President Waller reluctantly orders a nuclear strike. But before that can be done, Superman (obviously not Clark Kent) shows up and confronts Brainiac, whose nature is surprising and tragic.

Big
Steve Trevor has been sent on a mission to learn about a new weapon being developed by some bad guys. After he's captured, Wonder Woman (not Diana Prince) shows up to help him out. They take out all the bad guys, but not before the head bad guy activates the new weapon, which is a gigantic robot for which Steve is no match. Even Wonder Woman has some trouble with it, before finally beating it.