I love evil twins and mirror universes and undercover switching, so clearly this was just the thing for me. And the Injustice League was fantastic (I was particularly fond of Psycho Jaime), but I really fell kind of hard for Red Hood, with his tragic backstory and his slightly broken psyche and how he just kept going when the sensible thing would have been to fall down already. It would never have occurred to me that Earth-3 Joker would break my heart, but it genuinely makes all kinds of sense. I desperately want fic about this character now. (Is anyone writing B&B fic?)
Other comments:
* The opening scene is pretty effectively creepy; I would not want to see those guys advancing on me.
* Oh, look, the giant Joker card is the first thing we see in the Batcave. Subtle.
* "Suit yourself." *groan!* Took a second viewing before I got the joke.
* "Enough with the suspense, when do we pencil in the invasion?" Oh, Scarlet Scarab made me laugh a whole lot. Some days Chaotic Evil is all you really need in a villain (although it's a pain in the neck if you're their boss).
*Y'know, Bats really throws himself into the Owlman role; snarls and punches left and right. One wonders if he might have been enjoying himself just a little? He gets to deck Ollie for arguing with him and it's totally for the fate of the world! (The interesting thing is that this totally fails to allay Ollie's suspicions. Evil Ollie is smart!)
*Aw, Red Hood. Not just for the origin story (nice effect on the eye), but because he unhesitatingly listens to somebody who knocked him out and turned him over to his enemies to be tortured. (...um, actually, what was Batman's motivation there? It gets Hood into the Hall of Injustice, I guess...) And is then coherent enough to give directions in ways that actually sound like genuine responses to Cyclone's questions.
*...except it still doesn't work. This is why you get the robot to do the interrogation, I guess! (Seriously, I liked that, that the bad guys were keeping good pace with Batman's tactics instead of just hanging around being suckered.)
* "I have the heart of a hero." Yeah, torn between a giggle and a profound ick. And they say this show is fluffy... (Okay, compared to the DCAU it is, but still.)
*Batman almost punching Good Grodd; heh. These things should happen fairly often in mirror crossovers, reflexes and all... But it was the disgusted look Grodd gave him that really made it. (What is Good Grodd like, anyway? The sole peaceful and honorable member of a society of evil warlike gorillas bent on subjugation of the outer world? ...hm. So a gorilla Drizzt Do'Urden, then.)
* The ending made me laugh and laugh. Possibly definitely you should have gotten someone to watch over your evil twin while you were away, Bats, instead of assuming that he would be stopped by, y'know, locks and stuff. (Particularly it is unwise to leave your evil twin to be guarded by your own security system, which there's a better than even chance he'll know all the ways around.)
Also, the season (series?) finale of TMNT made me happy. It wasn't a stellar episode, but I'm a sap and I love big fluffy wedding stories that bring back everyone ever (Usagi! With lines, even!)--and hey, after twenty years Casey and April more than deserved their Big Day. There were some cute character moments ("I'm the maid of honor!" is vintage Mikey) and now I really want backstory on how Casey gave the Ninja Turtle Talk to his mom...