Mimbulus Mimbletonia. The plant Neville got from his Uncle Algie. Algie bought the plant while in Assyria. The plant is very rare-not even Hogwarts has one. The plant has a defense mechanism. Neville says the plant can do loads of things but what? Please note that Mimbulus Mimbletonia is the ONLY password for Gryffindor tower for the entire year.
Somethings to think about:
Neville wants to breed the plant-why?
There is a real plant called the Mimulus plant. Its essence is sold in England to cure fear of unknown things and shyness. Could this be a use for Neville's plant?
They always have several passwords during the year. This is the only year that there has been only one. That plant has to be something really big in the next book.