From the Super Mario Wiki
Smorg is the sixth major boss of Paper Mario: The Thousand-Year Door. Its name may come from the word smog, based on its dark, cloudy appearance, and the term miasma, referring to a poisonous cloud and/or dangerous atmosphere, likely referencing the appearance (the "tentacles," specifically) and hostile nature of the Smorgs. Their vocabulary consists of one word, "Smorg".
This boss does not hold a Crystal Star, but it attacks the Excess Express during the track to Poshley Heights. This boss is made up of massive horde of smaller Smorgs and the base was made up of Magenta Smorg. The appearance of the smaller Smorgs somewhat resembles that of Fuzzies. They are first seen at the Riverside Station, where they lift the drawbridge to stop the train from going far (it is unknown if it is working for the Shadow Sirens to stop Mario and his teammates from reaching the Garnet Star). Later on, they stow away on the train and kidnap the passengers. Mario and his teammates fight the Smorgs on the rooftop of the train to rescue the passengers. When they are defeated, they will blow away in the wind and release the passengers.
At the beginning of the battle, three tentacles will surround the main body, and near the end, they are replaced with a pincer claw that can do a large amount of damage to Mario and his partner.
Names in other languages