'If you're a billion dollar company advertising your game, ask permission!': Charlie the Unicorn creator chews out Warner Bros after MultiVersus ad uses his work without approval

They didn't need to ask permission, you couldn't do anything to stop them anyways.

But if you dare steal from them, even when it technically isn't theft, they will come at you with everything they got.

From the article:

In case you're not clued up on your 2000s internet lore, Charlie the Unicorn is a four-minute animated video featuring the titular horned horse as he ventures up Candy Mountain [...]

I'm guessing the author isn't clued up as well. It's a small series and watching the whole thing takes about an hour.