Supergirl Returns #12 - previous stories in this series are
On Twisting the Hellmouth
On Archive of Our Own
It may help if you've read at least the previous story, Five Dates Supergirl Didn’t Enjoy… And One She Did.
This is a (deep breath) DC Movieverse / DC Comicverse / Avengers Movieverse / Stargate SG-1 / Young Wizards crossover.
Cat Chaser (1/2)
Cat Chaser (2/2)