(5!!) Rounds of interviewing for a job they were supposedly urgently hiring for.
Each interview (outside of HR) turned into a consulting session where the interviewer didn't ask about skills or really experience, but wanted feedback on current systems, where to improve for their customer base, and what I'd do in their position. Trying to solve their business problems that they didn't have an answer for and wanted my ideas. Their final rounds include a "behavioral" check and also on on-site project from the hiring manager. Quite heavy for the role and projects could also be used to provide free material/strategy.