Well, just based on the cameos in the film, we have Looney Tunes, DC Comics, Mad Max, The Matrix, Harry Potter, Casablanca, Game of Thrones, Austin Powers, The Wizard of Oz, King Kong, The Iron Giant, Rick and Morty, It, A Clockwork Orange, The Devils, Gremlins, Beetlejuice, Hannah Barbera, Animaniacs, Lord of the Rings, The Sopranos, Thundercats, The Goonies, What Ever Happened to Baby Jane, Wild Wild West, Smallfoot, and The Mask. And I know WB also owns Cartoon Network, Tom and Jerry, and all the old Midway Games (which were all conspicuously absent from the film imo). They also currently have exclusive licensing rights to Godzilla in American film and POSSIBLY Pokémon if Detective Pikachu is anything to go buy. Honestly I think any of these are fine to use as long as we avoid using explicit violence, language, or XXX activities.