Around the line "I don't have time for a science lesson." (after the Substitutes contact Brainiac 5 for the first time), if you watch Brainiac 5's hands, you'll see his ring is missing.
After the Substitutes contact Brainiac 5 for the first time, another error appears. On the line "What's the important news?", his flap (the name they gave the character's speaking action) doesn't match his line.
When Chlorophyll Kid was introducing himself, Superman was supposed to say "Thanks for auditioning" only. Instead, he said "Want to show us what you can do?" at the point he was supposed to say the previous line. If you watch his mouth, you'll see it doesn't move when he says "Thanks for auditioning", and the line "Wanna show us what you can do?" doesn't match his lip movements.
(Stone Boy lands on Starfinger)
Infectious Lass: Phew, that was close.
Porcupine Pete: Yeah. Lucky you landed where you did.
Stone Boy: Lucky? I had to calculate the exact trajectory of my descent while vectoring in air pressure, wind speed, not to mention... (everyone is staring at him) What?
Porcupine Pete: You're talking...
Starfinger: Who are you?
Porcupine Pete: We're... y'know, we never did pick a name.
Infectious Lass: Uhh... Pete? Villain?
Porcupine Pete: Oh, right. Let's get 'im!
Superman: Hold on a sec, let's see what the new guys can do.
(Matter-Eater Lad ends up eating it)
Matter-Eatter Lad: Taste like chicken.
Bouncing Boy: Well I hope he saved room for seconds.
Brainiac 5: You can call off your plant now.
Chlorophyll Kid: Oh, I just make plants grow fast, but I can't control them.
Lightning Lad: And so it begins…
Saturn Girl: Can't you do anything to stop this thing?
Chlorophyll Kid: Would it help if I made it bigger?
Lightning Lad: As for the rest of you, better luck next time! (aside) As long as there isn't a next time.
Color Kid: I mean, I turned Superman lime green! That was dumb. If I had turned him forest green, I know I would've gotten in.
Bouncing Boy: You know, I failed my first audition too.
Infectious Lass: Really?
Porcupine Pete: Actually, according to the official collector's edition of the Legion Log, it took you four tries to get in.
Bouncing Boy: Yeah, well, keep trying.
Brainiac 5: Whatever it is, it seems to be feeding on the ionosphere.
Superman: I take it that's a bad thing?
Color Kid: Some chartreuse should stop you! No? How about magenta! Taupe! Lavender!
Starfinger: Oh. Who are you people? Seriously, do I owe you money or something?
Porcupine Pete: We're the… heroes that are going to take you down!
Porcupine Pete: How do we get your glove off?
Starfinger: I'll never tell!
Porcupine Pete: Ahh, come on, why not?
Starfinger: Well mostly because I… never figured out how.
Porcupine Pete: We saved the world?
Brainiac 5: Not yet. (fires the energy weapon) Now you saved the world.
Superman: We'd be honored to work with you again.
Porcupine Pete: Wow, you hear that, guys? Nothing could ruin this moment.
Pete's Mom: Peter! It's past your nap time.
Porcupine Pete: Except that.
UK airdate: 17th March, 2007.
Also appearing: Starfinger
The Legion of Substitute Heroes makes its first official appearance. Members presented here are: Chlorophyll Kid, Porcupine Pete, Infectious Lass, Color Kid, Stone Boy.
Additional Legionnaires who appear without dialogue: Phantom Girl, Star Boy (inducted this episode), Timber Wolf, Element Lad, Tyroc, Blok, Sun Boy