“I’ve said this before, but Velma in Mystery Incorporated is not bi. She’s gay,” the producer wrote. “We always planned on Velma acting a little off and out of character while she was dating Shaggy because that relationship was wrong for her and she had unspoken difficulty with the why. There are hints about the why in that episode with the mermaid, and if you follow the entire Marcie arc it seems as clear as we could make it 10 years ago. I don’t think Marcie and Velma had time to act on their feelings during the main timeline, but post reset, they are a couple.”
– Scooby-Doo! Mystery Incorporated producer Tony Cervone confirmed Velma Dinkley was written as gay, though they could only show so much 10 years ago.