Treasure of Swamp Castle is the English-dubbed name of the movie Szaffi, a 1985 Hungarian animated film from Pannonia Film Studio, directed by Attila Dargay (the person who also gave Hungarian audiences another beloved cartoon, Vuk The Little Fox). It is based on, and has music from, Johann Strauss II's operetta The Gypsy Baron—which is based on the novel "A cigánybáró" (The Gipsy Baron) 1885 by Mór Jókai.
Dragon with an Agenda: When the Governor is about to shoot Jónás and Szaffi, Puzzola reveals he's a Not-So-Harmless Villain: he knocks out the Governor by opening his high pressure valve, takes his gun and attemts to claim the treasure for himself.
Expy: The protagonist, Jónás looks very similar to the titular character of Ludas Matyi, an earlier animated film of Attila Dargay. In Hungarian, they share the same voice actor too.
Baron Loncsár, like the antagonist in Ludas Matyi, is also a Fat Bastard aristocrat, and the two characters also share a voice actor.
Harmless Villain: The Governer's henchman Puzzola has multiple murder attempts fail.
Not-So-Harmless Villain: While clumsy, Puzzola is a lot smarter and probably a lot more mean than the Governor, as he is the one suggesting him to kill the boy. He is admittedly an "intellectual criminal" rather than a murderer. And in the end he turns against his master to claim the treasure for himself.
Of Corsets Sexy: The Baron's daughter. Played for laughs, since she's rather unattractive otherwise.
Please Shoot the Messenger: In a variant, after Jónás fails to ask out the Baron's daughter, the father sends a letter via messenger pigeon to the Governor that he should kill Jónás. Szaffi the cat, however, attacks the pigeon and takes it to Jónás, who decides to deliver the letter himself, turning it into this situation.
Roma: The protagonist's surrogate family. Possibly the old lady in the swamp too.
We Named the Monkey : A plot point, since the protagonist thinks the black cat is Szaffi because they share the same name. Subverted in that Szaffi, the girl is named after her baby sneeze, but it happens to be the same as the name of the old lady's cat.