Batman's armor is the prototype for the Batman Beyond suit
A red and black full-body armor with retractable wings? Come on.

Supergirl was in Gotham when the Legion of Doom ambushed her...
... because she wanted to check on Batgirl and ask her help to find her cousin. Since this universe is based on Earth-One, Kara and Barbara are still friends here.

Pa and Ma Kent are dead in this universe
Superman was said everyone he cared about were kidnapped. We see Lois, Jimmy and Supergirl... but Pa and Ma were not seen.
Alternate explanation: They were off-panel.
Another alternate explanation: Pa and Ma were not kidnapped because the villains are fightened of Martha Kent.