Ug

Ug is the ninth boss in Luigi's Mansion 3. He is on the ninth floor, which is the Unnatural History Museum. He possesses a T-Rex fossil in the museum. Luigi will recieve the basement two's elevator button after defeating him. However, Ug doesn't guard the elevator button directly, the Blue Toad has the button. He has 400HP.

Appearance
Ug appears to be a yellow ghosts with muscles. His clothing shows that he is similar as a caveman. Ug has a hunched posture, black hair, and red eyes.

Battle Phase One and Two
When Luigi enters the museum and tries to save the Toad, the fossil of the Tyrannosaurus Rex comes to life and swallows the Toad's painting. To attack the Tyrannosaurus, Gooigi has to be eaten by the T-Rex, when the T-Rex rises its head, Luigi can get an egg from the fossils of pterosaur and shoot the T-Rex's chest. Luigi can also attack by throwing an egg to the T-Rex's mouth, it will try to swallow it and rise its head, Luigi shoot its chest now. After two hits the battle will get into phase two. Phase two is similar to phase one, but the Tyrannosaurus breaks free and Gooigi must sacrifice himself, and Luigi can only fire dinosaur bones at it. The fossil of the Tyrannosaurus Rex will be destroyed after four more hits.

Phase Three
During phase three, Ug will reveal himself and use a bone club to smash Luigi. Wait for him to use the shockwave slam, Luigi has to avoid it by a Burst, now his club will stuck in the ground. This is the chance for Luigi to flash and suck Ug up.

Trivia

 * Ug is the only boss who didn't show himself during the start of the battle.