It's called MultiVersus and it's a free to play, it's basically Super Smash Bros. with WB characters.
The starting line up includes:
Bugs Bunny
Shaggy
Arya Stark
Rick Sanchez
Morty Smith
Black Adam
Joker
Marvin the Martian
Gizmo from Gremlins
Stripe from Gremlins
Banana Guard
Jason Vorhees
Lebron James from Space Jam A New Legacy
Taz(manian Devil)
Velma
Batman
Bugs Bunny
Finn from Adventure Time
Jake from Adventure Time
Raindog (the game's only original character)
Steven Universe
Garnet
Superman
They're going to be adding more characters later, with Agent Smith already available early if you complete a themed "Rift" whcih are serious of PvE fights and other 2D platformer style levels.
Here's a Joker gameplay trailer
Looks fun but really not my cup of tea