The hippo-themed burger restaurant that Penumbra and the kids eat at in the amusement park is based off the Hamburger Hippo restaurant from Darkwing Duck (1991) which was first seen in the episode Getting Antsy (1991).
It can be implied that this episode was the first time where Webby had been able to eat a Hamburger, which was one of the many things she wanted to do when finally ready to enter the outside world as mentioned in the series' first episode.
Penumbra states to Launchpad her reason why she doesn't want to date him is that she has no interest in Earth men. It was stated by writer Sam Witwer on Twitter that Penumbra is actually a lesbian.
Timmy Jenkins previously made a brief cameo in the episode "Daytrip of Doom" as one of the kids seen at Funzo's Funzone.
Lunaris' ship can be seen floating past the moon at the end of the episode.