Despite following some critically acclaimed Marvel cartoons, The Avengers: United They Stand is often considered the worst Marvel animated property ever made. The series has a lot of issues thanks to its horrible visuals and writing. Due to its lackluster popularity and Marvel's financial woes at the time, the series was canceled, but the showrunners had plans for a second season, with several plot points having the potential to undo the show's biggest mistakes.
The Wider Marvel Universe
United They Stand would have solidified its connection to the general Marvel Universe much more in the second season with founding Avengers, like Captain America, playing a larger role. Cap, who previously had a single episode in the first season, would come back for a two-part storyline. This likely would have been to make up for how Cap's Season 1 episode acted as a backdoor pilot for the Captain America cartoon, which was no longer going to be produced.
Thor would also get a two-part story involving Loki, and Bruce Banner would show up when Ant-Man was affected by gamma radiation. Furthermore, existing cast members would have been fleshed out more, with Hawkeye returning to the circus and Scarlet Witch revealing the origin of her powers.
Perhaps the biggest selling point for this second season was the planned appearance of the X-Men. It wasn't specified which mutants would be included, but the idea was to have the voice actors from X-Men: The Animated Series reprise their roles in United They Stand. With some of those actors already working on United They Stand, this suggests the main X-Men team might've been featured in Season 2.
Improving the Avengers' Roster
These ideas would have whittled away at the show's biggest issues. For instance, many viewers hated that the show chose to fill its roster with obscure heroes instead of focusing on characters like Captain America, Thor and Iron Man. Cap and Iron Man did have appearances in the first season, but they were under utilized. By bringing in these bigger heroes for larger roles, it would have given the show more of a draw. The same could be said for incorporating members of the X-Men, who were immensely popular at the time thanks to their show.
Giving more depth and backstory to the existing cast would have also made viewers more inclined to like this version of the Avengers. Many felt the heroes featured in United They Stand were flat at best and annoying at worst, particularly Hawkeye. Giving spotlight storylines to each hero was part of what made X-Men: The Animated Series such a hit, so doing the same for United They Stand would've hopefully seen the same results.
These plans may not have erased how bad the first season was, but if produced, it could have salvaged the show's reputation as a whole. This was the case for the Iron Man and Fantastic Four cartoons of the '90s, which got second seasons that were seen as improvements over their less celebrated first seasons. Sadly, The Avengers: United They Stand was never able to make the same course corrections.