George & Harold in The Loud House: The Batman/TMNT Adventure

George & Harold in The Loud House: The Batman/TMNT Adventure is a 2018 digitally-animated 2D action-comedy released by Warner Bros. Feature Animation and Nickelodeon Movies. The film is a four-way crossover between The Loud House, Teenage Mutant Ninja Turtles, Captain Underpants, and Batman: The Animated Series, though it is based on the 6-issue miniseries Batman/Teenage Mutant Ninja Turtles Adventures.

Voice cast
Additional voices include Jeff Bergman, Rob Paulsen, Tom Kane, and Jill Talley.

Plot
The film begins with Harold being driven back to the Louds' neighborhood by Bumblebee and Sari Sumdac, following a battle against Headmaster (who apparently returned a FOURTH time). However, due to misreading the situation (when Sari gave Harold a quick kiss on the cheek as he got out of Bumblebee), Maggie (the emo teen from "Funny Business") whacks him in the head with a baseball bat, which results in Harold screaming a series of angry curses at her, though Luan manages to clear things up between them, leaving behind plenty of lingering awkwardness.

Later, in Manhattan, Turtle Titan (Michelangelo) attempts to intimidate a bank robber, who passes out afterward. Back at the Lair (where the Loud siblings and Clyde have gathered), Leo is lecturing Mike that they can't allow themselves to be seen, when Donnie's laptop picks up a portal signal, meaning only one possible thing—the Kraang have somehow returned...

While staking out the sewers, the team encounters Clayface, who's all-fired-up and pissed as hell. After a brief battle, Donnie forces him through a portal by blasting him with a storm drain.

Meanwhile, Batman's archenemy, the Joker, and his gun-moll Harley Quinn, have recently escaped Arkham Asylum and encountered Shredder, Bebop, Rocksteady, and Ch'rell. After Joker explains his story, Shredder orders Bebop and Rocksteady to deal with their unwanted guests, but Joker quickly stuns them with an explosive rubber chicken. Ch'rell, in a makeshift exosuit, makes short work of the Clown Prince of Crime and advises Harley that this was just a warning and that next time Joker steps out of line, he won't be so lenient.

In Central Park, the team discovers another portal, from which Batman, Robin, and Batgirl emerge. Mistaking them for Dimension X mutants, the team attacks and a battle begins. Eventually, Bat-Mite appears and breaks up the fight by explaining that they are all on the same side. Any further competition is cut short when the team discovers Snakeweed and Poison Ivy, wreaking havoc on unsuspecting joggers.

While the others keep Snakeweed and Ivy at bay, Harold transforms into Grey Matter and constructs a "retromutagen grenade", which he throws at Snakeweed, changing him back into his human form, Snake Weedelman, who falls unconscious after his de-mutation.