Superman II - After bring sucked into the crib vortex, Foop is seen flying in a flat glass-like plate. This is a reference to the Phantom Zone where General Zod was banished into space by Superman.
Playskull - Playskull is a parody of Playskool.
Foop does something bad, but when Wanda comes he makes it look like Poof did it and then cries. Wanda will get angry at Poof and take away a good star on Poof's good star chart.
Cosmo complaining about beets, and saying "Why does everyone hate me!?"
Wanda making Cosmo eat beets.
Many find it out of character for Wanda to take the word of Foop over the word of her own son when Poof said that Foop was trying to send him to a parallel dimension; especially as pointed out by Timmy, Foop tried to destroy two magical realms and a fast food chain.
After Cosmo wishes away the second vase on the welcome banner, it does not change movement. Later, the first vase disappears and the banner does not change movement still. Then, the banner is gone.
When Wanda says "The playpen is not an interdimensional vortex of doom.", the captions display AN with a D, as in AND. That would make Wanda's quote nonsense. Coincidentally, just before she said that quote, she added "Nonsense, Poof."
It is unknown how Foop escaped his previous imprisonment in a parallel dimension.