during the pilot of Hazbin Hotel, Lucifers personality was, different, his appearance was little different as well, being taller, with his hat and suit having minor changes. Unlike his personality, which was changed. His pilot variant was more stolen, serious, blunt and sadistic. His modern/show appearance, is cheerful, prideful, silly and egotistical.

The pilot and show universes of Hazbin, exist at the same time. Though being the same place, it's different.

Suddenly, the pilot, and show Lucifer swapped places. Lucifer (present), was now in the pilot for the show. And Lucifer (pilot) was now in the full show, what could go wrong?