User blog comment:Decca03/Scooby-Doo! Stage Fright – Review/@comment-1674355-20130614053742

There have been swords in Scooby-Doo as early as Go Away Ghost Ship (the sword was on a wire, but it still counts).

Romantic implications between Fred and Daphne were there as early as Scooby-Doo on Zombie Island.

And two or more independent villains in the same costume first happened in DC Comics stories Six is a Crowd. There have been several other such cases.