These are Danny Phantom, Helga Pataki (from Hey Arnold!) and Leonardo, Michelangelo and April O’Neil from the Turtles franchise. The videos can be seen below.
In Nickelodeon All-Star Brawl, which seems to offer a similar gameplay experience to the Super Smash Bros. games, several characters from Nickelodeon franchises battle it out. Other characters already announced include Spongebob Squarepants and Ren & Stimpy.
The game will be released on October 5 for Steam, PlayStation 5, PlayStation 4, Xbox Series X and S, Xbox One, and Nintendo Switch.