It's doubtful the fake air-filled Hall of Doom would have made it into space. No matter what size, a balloon will puncture if it gets too high into the atmosphere.
When Sinestro appears in front of Green Lantern in the subway tunnel, he comes in with a green glow instead of yellow. Also notice when he uses his power ring to produce the large spring that prevents the train collision, the energy discharge from the ring is also green just before the next shot shows the yellow energy that forms the spring.
Hal Jordan is obliged to teleport himself out of the subway car to conceal his transformation to Green Lantern. But it seems as if teleporting out in a green glow is just as obvious as if he had just transformed in the first place.
When Luthor transmits to the Hall of Justice that they will rescue the planet, when we see the Legion's viewscreen it shows us the SuperFriends seeing and hearing Luthor from the rear, facing the Monitor Screen. In other words, the Legion are tapping into a camera the Justice League has set up to show them from the rear. Who would want a camera that shows your backside?
When the Riddler transmitted his first riddle, his face was on the underside of the mock Legion of Doom ship. When the SuperFriends play the recording back, his face is projected in front of it.
In the subway when he confronts Sinestro, Green Lantern's costume is missing the neckpiece and he has partially-bared shoulders (like Superman's neck-area). Typically GL's costume covers his entire neck and indeed does so in the rest of the episode.
When the Flash breaks the Time Barrier he's running up in the sky.
When Bizarro attacks the future city, his cape briefly disappears.
Riddler: We'll slip through your fingers if you give us the room. So be very careful or you'll end up in a tomb.
Batman: (reading riddle left behind by The Riddler after escaping) You've escaped with your lives, but to us you're long dead. If you bet you find us, we'll be a dollar ahead.
Villians appearing without dialogue are Brainiac, Captain Cold, Cheetah, Giganta, Scarecrow, and Solomon Grundy.
Aquaman and Apache Chief have no dialouge in this episode.