Lara Croft was planned for the game, but Eidos declined on the grounds that they had different plans for the character and her Tomb Raider series at the time, presumably leading into the series' 2013 reboot.

The developers really wanted a character from Square Enix's Final Fantasy series to make an appearance, but Square Enix refused to loan their characters due to SuperBot being a relatively new team and the game they were developing being relatively new as well.

A prototype build for PlayStation All-Stars Battle Royale shows an early character select screen with a set of unused characters:

• Chop Chop Master Onion from the PaRappa the Rapper series
• Captain Blasto from Blasto
• Buzz from the Buzz! series
• A Big Kulche from the LocoRoco series
• Dr. Nefarious from the Ratchet & Clank series
• A Eucadian Soldier from Warhawk
• A knight from Fat Princess
• Um Jammer Lammy from the PaRappa the Rapper series

Notably, Dr. Nefarious is featured in the roster without Ratchet or Clank. PaRappa the Rapper is the most represented series in this roster, and has more characters than any one series would get in the final game including DLC. The knight would appear in Fat Princess' moveset, LocoRoco and Buzz! would be represented through stages, and Blasto would be absent completely.

PaRappa the Rapper co-creator Rodney Greenblatt had a bittersweet response to PlayStation All-Stars Battle Royale, appreciating that PaRappa was in a new title and finding the game fun, but disliking the presence of PaRappa in a battle game with lots of realistic weaponry.

When Hades appears in the Polygon Man boss fight, there is a rare chance that he will perform a dance akin to a cowboy swinging a lasso while spinning in a circle. This dance originated from the 1995 episode "Viva Lost Wages" of the TV series "The Fresh Prince of Bel-Air", where Will and Carlton are forced to enter a talent contest to win money to return home from Las Vegas. During the talent contest, they performed a dance set to The Sugarhill Gang's cover of the Jerry Lordan-penned song "Apache" (also known as "Jump on It"), and the dance in question was originally improvised by actors Will Smith and Alfonso Ribeiro prior to the episode's filming backstage. The cowboy portion of this dance would later be popularized around the time of PlayStation All-Star Battle Royale's release through an appearance in the music video to "Gangnam Style" by Psy. It is not known if there is any way to intentionally trigger this Easter egg.

The developers of PlayStation All-Stars Battle Royale expressed that they wanted Mario as a playable character in the game as a nod to the Super Smash Bros. series.