- Doing It for the Art:
- In order to get references for I.M. Weasel's mouth movements, Ian JQ had to access Cartoon Network's old site via the WayBack Machine because the physical copies of them were inaccessible.
- The team had to get legal requests for every cameo, which was a very long process, and they also went the effort of tracking down their model sheets so they'd match the art styles of their respective shows.
- Executive Meddling: The original pitch was for a half hour special, but CN requested they cut it down to the standard fifteen minutes, leading the crew to create a whole new plot to fit the timeframe.
- Exiled from Continuity: While the episode is dense with references and characters from the history of Cartoon Network, there were a few which couldn't make it in, due to various legal reasons and the short timeframe of the episode:
- Transformers Animated and the two Star Wars shows co-produced by Cartoon Network aren't in this, due to the properties being owned by Hasbro and Disney, respectively.
- No Warner Bros. Animation productions are represented other than Teen Titans Go!, despite the studio producing many series specifically for the network. Similarly, no Hanna-Barbera properties like Scooby-Doo and Tom and Jerry were included due to Warner Bros. having ownership over the characters.
- Concurrently running shows such as Ninjago, Sonic Boom, and Mega Man: Fully Charged were also absent, due to being owned by the LEGO Group, SEGA, and Capcom, respectively.
- Mixels, despite being classified as a Cartoon Network Original, is not included thanks to LEGO also owning a fraction of the franchise via the merchandise half.
- The Total Drama franchise isn't represented, likely due to co-ownership with Fresh TV, which presumably also applies to 6teen, Stōked, and GrojBand.
- Various third-party acquired shows, including anime, which had aired on CN at one point or another didn't make the cut.
- Only two CN foreign co-productions not broadcast on the U.S. channel were depicted, as detailed below.
- No Adult Swim shows were included due to the block being treated as a separate entity from CN, though a poster for Samurai Jack's Adult Swim-only 5th season did appear.
- None of the infamous live-action shows are represented except for Out of Jimmy's Head, likely due to it being a live-action/animation hybrid.
- Marth Debuted in "Smash Bros.":
- Throw It In!: The inclusion of Schnitzel, Illana, Jake and I.M. Weasel all came from their respective actors having fun in the recording booth voicing other characters of theirs.
- What Could Have Been:
- The episode was originally planned as a 22-minute special. The episode's plot was heavily re-worked after the decision to make it eleven minutes was made, including changing the setting of the episode officially to CN City and the creation of Strike. In the original pitch, Strike's Red Pen robot was the Big Bad, and was to hypnotize the heroes and have them fight each other. The original storyboards also featured K.O. meeting Ruby and Sapphire, and the picture behind Garnet while she's introducing herself also included Peridot and Connie.
- Class of 3000 and The Secret Saturdays were going to be represented, but the scenes with their cameo appearances got cut. Unlike the other shows on this list, this wasn't a legal issue: Ian JQ has stated that cameos were planned for both shows, but their scenes had to be cut for time. As seen in this tweet, Li'l D was planned to be Class of 3000's representative. Characters from those series eventually appeared in the series finale, "Thank You for Watching the Show".
- The episode resulted from the network originally proposing having past CN heroes cameo as students in the POINT Prep arc, with the crew believing that such a thing would be a waste when they could have an entire episode exploring the idea.
Trivia / OK K.O.! Let's Be Heroes S2E18 "Crossover Nexus"