Ug

Ug is an enemy ghost encountered in Luigi's Mansion 3. Ug is a brute caveman ghost that resides on the Unnatural History Museum located on the ninth floor of the hotel. He serves as the ninth boss of the game and Luigi has to fight him for the Basement 2's elevator button.

Biography
When Luigi finds Blue Toad inside room, he tries to release him from the portrait. However, the T-Rex behind him attacks him and eats the whole portrait and hides it inside his skeleton. Luigi has to fight the T-Rex by throwing it artificial dinosaur eggs that will have stuck on its mouth, this makes the T-Rex reveal its core and Luigi has to throw another egg at it, causing damage to the T-Rex. It will try to cause some rocks from the ceiling to fall on Luigi. When Luigi hits the T-Rex for the second time. It finally breaks free from where it is restrained and goes on its way around the room to kill Luigi. Gooigi can be summoned to take care of the dinosaur by using the rest of the fossils that the T-Rex destroyed to throw them at it. After damaging it enough, the T-Rex will finally collapse and be destroyed.

However, a caveman ghost emerges from the ruins of the skeleton, revealing himself as the one possessing it the whole time. He is angered at Luigi for destroying the T-Rex and prepares to battle him with his massive bone that uses as club. Ug will swing his bone to harm Luigi and even charge and slam at the floor creating an energy wave that damages everything and everyone on the ground. In order to defeat Ug, Luigi has to flash Ug in the right moment he gets his club stuck to the ground which allows Luigi to vacuum him. After getting defeated, Ug will throw his club in the air and humorously have the club land on his still-exposed head before being sucked in. After Blue Toad is released, he reveals having the elevator button to Basement 2.

Trivia

 * Though his real name is Ug, in the Dutch translation of the game he is literally called T-Rex.
 * He somehow resembles Marvel's superhero Hulk given his short hair, green skin and massive strength.