Rachael is wearing a fish costume and is infected with an adult Diphyllobothrium latum, commonly known as the broad fish tapeworm. Yes, she technically would have the larval form rather than the adult worm, but hey, she gets extra bonus points for the excellent morphology of her worm. Note the 'spoon-shaped' scolex and the wide proglottids with central rosette-like uterine structures. Each proglottid was attached using Velcro, so she could 'shed' whole segments of proglottids at a time.
Her Giardia duodenalis cupcakes were delicious, just like her botfly and Dracunculus medinensis cupcakes from last year.
Heather delivered up Cryptosporidium pizza for all, along with her son who came dressed as a slice of pizza.
Lastly, you all guessed it - I was a snail shedding Angiostrongylus cantonenis larvae. Rats are the definitive host, whereas humans are accidental hosts and can get eosinophilic meningitis when accidentally ingesting larvae in infected snails, slugs, and slime. Cats aren't a known paratenic host, from what I could find in the literature, so my cat was probably fine.