Prug is a dragon and the older brother of Grup. He formerly served as the Guardian of the Boulder Magisword until it was retrieved by Prohyas and Vambre and now works at the Cave of Stuff as a cave dragon alongside his brother.
Prug is nearly identical design-wise to Grup, with subtle differences such as a thicker tail and a lower-hanging nose. He is also much larger than his younger brother, even towering over the Warriors for Hire
Prug is usually content to stand in the background compared to his other cave monsters. In many ways, he is very similar to Grup, including low intellegence and a habit of jumping to conclusions. Unlike his younger brother however, Prug is considerably slower, quieter and soft-spoken, rarely talking unless someone has spoken to him first. He is also slow to act, often requiring Grup's encouragement to move into action.
He first appeared in "To Boulderly Go" inside a cave, where Vambre and Prohyas approach him for the Boulder Magisword. They ask him if they can have the sword, in which he willingly agreed. After Prohyas used the sword, it generated a boulder that sealed the cave, trapping them all inside. Prug suggested to play hide and seek despite the fact that it's impossible to do so in the cave. Its revealed in "Random Acts of Memory" that Nohyas freed the three from the cave, right before Nohyas made them forget Prug existed.
He appears in the short "Working Grup", alongside Grup and his Cave Weirdo friends in the Cave of Stuff. Grup introduces him to Prohyas and Vambre and he acknowledges that he had been trapped in a cave with the two before, but Prohyas and Vambre have no recollection of the event.
Prug makes his first re-appearance since the series' first short in "Cleanliness Is Next to Grupliness" commenting on Skulliver's jar-ham nose.
In the episode "Biggest Fan", he and Grup served as sharks in the Cave of Stuff for Glori to get the Warriors to save her. He later brings Glori to the Warriors since they want her to leave due to her being a terrible actress.
He and the other Cave Weirdos made a slight cameo in "Little Sword of Horrors" where they tee pee Prohyas watering his Carniverous Plant Magiseed.
- Prug appeared in No Robots for Old Men, alongside Old Man Oldman and Robopiggeh. However, he was referred to by the other characters as Grup, who had not yet been introduced in the series. The size and voice of the appearing Dragon however that of Prug rather than Grup.
- Originally, Prug spoke in a very plain deep voice, and maintained this voice throughout the 3 minute shorts. After Grup was introduced however, Kyle A. Carrozza changed Prug's voice to better resemble his brother, using a deeper version of Grup's voice for Prug.
- In For the Love of Narwhal!, it is revealed he also has tiny wings like Grup, but it is unlikely he can fly with them possibly because of his size.