Voice acting is included in a 2022 update of the game.
Shortly after the game's announcement, Youtuber Uncle Al (known for his impersonation of Hugh Neutron from Le avventure di Jimmy Neutron (2002)) started a joke campaign to get Hugh into the game as a playable character. The movement became very popular, to the point of gaining support from Hugh's original voice actor Mark DeCarlo. In May 2022, Hugh was confirmed to be coming to the game as purchasable downloadable content, with DeCarlo reprising his role officially for the first time since 2006.
"You wouldn't like my brain, it's all circuity and metallic" was removed after a quick patch for Jenny Wakeman due to the quote being associated with Zone's pornographic parody called What What in the Robot, but with "body" in place of "brain".
Out of all the available characters, Powdered Toast Man, Oblina, Nigel Thornberry, Aang, Toph and April O' Neil are the only characters to not have their voice actors reprise their roles due to them being unavailable, retired or deceased.
Grandpa Lou can be seen in the background of the Showdown at Teeter-Totter Gulch level.