After the Guys in White capture Sam and Tucker, one of them calls them "meddling kids," an allusion to the Scooby-Doo franchise.
Danny riding Johnny 13's motorcycle reflects Danny's original character concept, where he would have ridden a motorcycle and used gadgets to hunt ghosts instead of having super powers.
This is the only time in the series in which Vlad appears as Vlad Masters but not as Vlad Plasmius.
When Jack and Maddie buy back Fenton Works, the giant check they bring with them is for one quintillion dollars. This is more money than what currently (as of 2019) exists.
Butch Hartman's signature can be seen on the hundred-dollar bill in the title card.