Before the Stormchaser
He was recruited when Quintinius saw his brave fighting skills and his fierce nature. Quintinius saw him as loyal but somewhat disreputable. Quintinius did not fully trust Mugbutt, and for this reason he had him chained up, shackled to trees or the mast whenever they slept.
Mugbutt was a very good friend of Spleethe's and took to reciting his last words back at him, for instance, when Twig first met Mugbutt and Spleethe, Spleethe said: "It seems, our friend Mugbutt, that our captain has over-reached himself," and Mugbutt said "Over-reached himself!?!" Also during the mutiny Twig heard, all Mugbutt did was repeat what Spleethe said, i.e. Spleethe said "Claim the rewards" and Mugbutt said "The rewards!" gleefully.
Spleethe and Mugbutt were indeed planning a mutiny on the ship. Spleethe would kill Quintinius, and take his place as captain, and Mugbutt would be his lieutenant and second in command. They would take stormphrax back to the League of Free Merchants of Undertown and would split the money fifty-fifty.
Mugbutt was assigned to looking after Twig, during Spleethe's attempt at smuggling Twig on the ship when Quintinius had told his son Twig not to come. Twig wanted to, so he disobeyed. Mugbutt was his guard, and he was a filthy goblin, because he never ever washed and left his food abandoned in corners.
Mugbutt sniggered occasionally during the voyage and said "Too rough for you is it?" Twig didn't reply and when the Storm knocked Twig unconcious, Mugbutt smirked down at him and said he would be watching over him, laughing evilly.
Twig woke to hear Spleethe and Mugbutt discussing the mutiny. Twig was alarmed and sought to alert the crew, but they couldn't hear him and were busy keeping the ship airborne. Mugbutt noticed Twig attempting to escape but he was too slow to stop Twig running out the hatch and on deck. Mugbutt ran out after him and conversed with Spleethe, arguing about how Twig was difficult to guard and would be the bane of the mutiny.
Mugbutt approached Quintinius and demand he surrender his post. Quintinius demanded "WHAT? But this is mutiny!" He then argued with Spleethe about how Simenon Xintax wanted Spleethe to fail, which Spleethe screamed "He's lying" and then demanded Mugbutt's help. Mugbutt leapt at Quintinius and a furious battle began which was made epic by the lightning flashing round them and the thunder. Mugbutt was a formidable fighter and he got the upper hand, but Twig called out to Hubble the banderbear to help. Hubble eventually leapt down, knocked Mugbutt aside, just when he was about to stab Quintinius in the throat, and Hubble knocked his paw down on Mugbutt, killing him.