Scooby-Doo, Where Are You! was a Saturday morning Hanna-Barbera cartoon that first aired on CBS in 1969. The iconic characters and episode structure have come a long way since the '60s, reimagined in dozens of shows, movies, and cameos. Crossovers, in particular, hold a special place in the franchise, as several real and fictional guest stars have arrived over the years to lend the Mystery, Inc. gang a hand. That trend began with The New Scooby-Doo Movies: only the second series in Scooby-Doo's long run, premiering in 1972. It featured a new guest each week, tangled up in the mystery du jour. They were often real-life celebrities, and young fans likely had no idea who they were, but they became part of the franchise's DNA.
Source：https://www.cbr.com/scooby-doo-favorite-crossovers/
