If I were writing GREEN LANTERN, now that Hal's GL again, I'd introduce the secret villain. You know the type, the guy who's revealed to have been part of continuity for years, but always behind the scenes, whose appearance ties together all the loose ends that fans have wondered about.
This would be the guy who's had a grudge against Hal for years. Another test pilot, maybe, one who officially died in space but was actually torn from his body and given a terrifying new power. He's tried to kill Hal Jordan more often than anyone, and he's come closer than most. The brain damage Hal suffers from is entirely due to this guy's efforts to end his life.
The villain's only power is the ability to possess inanimate objects. Every tree branch, every bar of soap, every low doorway that's ever given Hal a surprise concussion... that was all him. You fools thought that one man could so often defeat alien armadas and yet succumb to ordinary household items? Ha! And now, now the masks are off, now he will reveal himself and his TRUE plan, which et cetera. You know the story.
Look me in the eye and tell me this wouldn't explain a lot.