Just a little PSA because I saw some confusion.
When the website says there are 66 characters, there's a little asterisk that says the Pokemon Trainer is counted as one character, and the echo fighters are counted as separate characters.
So, we take Ridley's number, 65, subtract two for Pokemon Trainer, then add three for Lucina, Dark Pit, and Daisy. We got 66 fighters, it's not a leak or a mistake.
You wanna know what is a mistake? Olimar's page calls him "Olimer" in the background text.
EDIT (the proof):