Actually got the idea from those group shots you see in fighting games or RPGs, where the whole cast is shown as a unit. You usually see them in games with a ton of characters... but hey! 1990s family sitcoms had a ton of characters, so why not?
A lot of Street Fighter and Kingdom Hearts were used as reference for the composition, among other games:
All works copyright of their respective owners, of course. Namely Capcom and Square Enix.
Always loved group illustrations like this though, you get a feeling of the importance of the characters as a unit. Sadly it seems like we don't get a lot of games that emphasize huge all-star character casts anymore; it's more common to see at most a duo, or solitary protagonists fighting by themselves shown on the game's cover. I would love to see more titles with boxart using this sort of layout though.
I think I've done all I can in Photoshop with this, so it's time to do all of the fancy linework in Illustrator.