Thugly is the boss of Cliff in Donkey Kong Country Returns who appears to be related to Mugly, the boss of the Jungle world.
Thugly looks simlular to Mugly, except he has iron plates on his back (simlular to those on an armadillo), and he has sharper teeth and purple skin. His eyes are red, and also has sharper horns. Basically he's just a much harder-to-fight Mugly.
When Donkey and Diddy Kong blast up into a lair in the mountains, they see Thugly munching on their bananas. Suddenly the Tiki Tak Tribe appears and a Tiki that looks like a xylophone hypnotizes Thugly to fight the Kongs, causing the battle to begin. The battle is very similar to Mugly's. In all states, Thugly will dash, curling up his plates every time he skids. When the plates on his back stay open, you must jump on his back. In all states he will quickly charge into the wall that far from him and cause rocks to fall, thus becoming dizzy and falling onto his back, after which you must jump on his stomach. He also will leap up and crash down near you, producing a harmful shockwave. After three hits, he will become orange. In this state, he will be able to shoot a stream of fire (like a dragon) that extends all the way across the arena, which you must duck under. After three more hits, he will become red, and he will now be able to spit meteorites. The meteorites split into three smaller ones while in the air. After each state transition, he crashes through the floor, bringing the Kongs and himself nearer to the bottom of the canyon. After beating him, DK will punch the xylophone Tiki and end the stage.