“Monetary wealth gives me freedom, and freedom gives me wealth of spirit!”
Flavio is a 25-year old "famous" Rogueport entrepreneur. He has in his possession many fine ships, his favorite being the S.S. Flavion, which he and Mario used to travel to Keelhaul Key. It was unfortunately destroyed in the very same voyage. He enjoys believing that he is a fearless, brilliant man that others idolize and envy, but he is not particularly popular among his crew, or anyone, as a matter of fact.
Mario first meets Flavio at Podley's bar with his prized possession, the Skull Gem, whose help Mario and his friends needed to get to Keelhaul Key in order to obtain the fifth Crystal Star, asks Mario what it is that he lacks despite being the richest possible man in Rogueport (those being emotions, money, romance, or thrills). After Mario answers, Flavio comments on what Mario said he lacks. Flavio then touches on the subject of Cortez's treasure hoard, saying that many ruffians and treasure hunters have all went to Keelhaul Key for that goal, only to never be seen or heard from again, which is why no other sailor dared try to step foot on the cursed isle.
However, he does not let mere rumors stop him from claiming the treasure of Cortez. Mario then asks about any possible treasure in Rogueport, but Flavio scoffs at him saying there was no such treasure there, and tells Mario not to believe in words that the local street urchins whisper. Mario decided to prove his point by showing Flavio his Magical Map, and Flavio realizes that there is a mark right where Keelhaul Key is located on the said map. Then, he accuses Mario of trying to get the treasure of Keelhaul Key before him, but Mario then says the only reason he is trekking to Keelhaul was for the Sapphire Star. Flavio then calms down and says that he heard about a "star-shaped stone" amongst the vast hoard of treasure, but even then Flavio says the rest of the treasure will belong to him but Mario may have the Sapphire Star.
Mario then tells Flavio that he does not own a ship to sail. Flavio then says that he has his own ship and tells Mario to go prepare himself for the voyage and meet Flavio at the harbor and Flavio calls himself the intrepid leader. However, when Mario has finished preparing for the trek to Keelhaul, meets Flavio at the harbor, and after Flavio introduces his S.S. Flavion, there has been a slight error of sorts. That error was that the S.S. Flavion had no helmsman to steer the ship, due to the fact that the previous one ran off. Flavio then said to Mario that even if Mario should find a helmsman to the steer the ship, then that person would also have to be absurdingly masterful at the job because the waters of Keelhaul Key spelled out death, which was the major problem.
Pa-Patch, a salty Bob-Omb sailor who has joined the voyage, speaks about an incredibly skilled helmsman who could make any ship bow before him with the greatest of ease, but has not been seen sailing ever since his wife had passed away: Admiral Bobbery. Flavio then pins the position of Captain on Mario and the job of hunting down the Admiral for his help to navigate Keelhaul Key's waters.
After a chain of events to find Bobbery, and successfully obtaining Bobbery's help, Flavio then asks once more if Mario has any more preparations to make before shoving off. If Mario does, then Flavio will wait until Mario is ready, if not, then they shove off for Keelhaul Key without delay.
While they sail for three days straight, Flavio writes comments in his diary about how well the voyage is going so far. On the final sunrise, Flavio mentions he may have been eager to get to Keelhaul Key, he was scared at the same time, much due to the ghastly rumors he once heard from other men of the sea. On that very night, Flavio sings his song again and out loud. After Flavio is done, he then begins to recite his tale of bravery about being locked in combat with a lethal sea serpent (This is something the crew has already heard about). Knowing that Flavio will lose his temper if someone interrupts his yarning of his tale and that there's nowhere to escape to, they let him talk but Flavio is mostly tuned out thus is talking to himself. Flavio was also too absorbed in weaving his tale that he didn't realize that the ship had suddenly stopped and when Pa-Patch stops his tale midstory, Flavio calmly retorts that it was Pa-Patch's job to make sure the ship kept going. After Pa-Patch sees a ghost, Flavio does not believe it at first, but when many blue flamed ghosts appear and corner the S.S. Flavion, Flavio becomes a nervous wreck and tries to unsuccessfully calm his crew down. When a larger than normal Ember appears before Flavio, he asks if this particular one was the savage King of Pirates and his skin turns blue with fear as the ship sinks even further into the ocean.
The next morning, he is currently caught up in argument with Pa-Patch about being terrified of the Embers they've seen the previous night, but when Flavio is called a "Fancy Pants" by Pa-Patch, he just loses his temper, calls Pa-Patch a cyclops, demands revenge for his insulted pride, and a fight at dawn. However, just as soon as they leave the area to go take the fight somewhere else, they come back in a flash and terrified, as they have encounted more Embers. After Mario makes quick work of the Embers, Flavio now requests that Mario should go explore the island. If Mario should refuse, his decision is overturned by every one of the crew voting that Mario should definitely explore the isle, with Flavio saying that they couldn't just sit about idly and do nothing.
Admiral Bobbery's last wish was to drink his bottle of Chuckola Cola, which was in Flavio's possession (he had found it and claimed it as his own). Because the rich entrepreneur had found the Chuckola Cola first amongst the floatsam, despite the fact that Bobbery was dying, he does not hand over the beverage even then, the reason being is that he says it was part of the group's supplies, in which they needed to survive. If Mario could find something suitable for replacement, then Flavio would hand over the drink. When Mario returns with a Coconut, Flavio was obviously a little disappointed with the results, but couldn't expect much from a non-gourmet and keeps his word by giving Mario the Chuckola Cola. Flavio tells Bobbery to savor this delicious drink.
Later, Flavio temporarily joins Mario to go to where the skull rock lies, and although he says "no" at first, everyone votes against him, similar to what they did to Mario, and grudgingly goes with Mario. Flavio does not help Mario in battles if Mario runs across enemies while trekking to where the Pirate's Grotto is. Mario will request that Flavio hand over his Skull Gem in order to open the grotto and Flavio warns Mario to not run off with his prized heirloom. If Mario needs help on how to open the grotto, Flavio sings the answers in subtle hints, but Flavio never realized what the song truly meant. After Mario opens the cave, the Skull Gem seems to be ruined by Bobbery's explosion and Flavio mourns over it, but the Skull Gem survives the explosion and is relieved. Flavio then goes back to the camp site and leaves Mario to explore the grotto alone, wishing Mario the best of luck.
After Mario's scrap with Cortez over the Crystal Star, Flavio goes out to congratulate Mario along with the crewmen. However, the mysterious Four-Eyes is not amongst the crew. After exiting the grotto, they hear the sound of a cannon being shot and vibrations are felt. This is when Four-Eyes reveals his true self as Lord Crump and threatens to blast them to bits unless Mario surrendered the Crystal Star. Realizing that sailors are just sailors with no ship, Flavio then requests that Mario take him to Cortez so that they may use his ship, the Black Skull. One Toad tries to stop him by saying that Cortez could possibly kill Flavio and may not even lend the Black Skull to him just because Mario defeated Cortez. Flavio then admits he may be nothing more than a big chicken and attention seeker, but Flavio refused to back down and compromise the lives of his crewmen or anyone else involved in this and again asks Mario, without any doubt in his mind, to escort him to Cortez.
When Mario returns with Flavio, Cortez reappears and asks Mario if he has forgotten anything more. Although that pure terror was painted all over Flavio's face upon setting eye on Cortez, Flavio gathers the courage to ask if he and his crew may borrow Cortez's ship and when asked his name by Cortez and what would make Cortez think he'd just hand over his ship, Flavio reveals his name to Cortez and then explains the situation so far: his crew were in danger of becoming blasted to pieces by the cannons of the X-Nauts' ship, and they really need a ship for protection and as a means to retaliate. Cortez just scoffs at Flavio's request, saying that Cortez doesn't lend a ship just for the sake of pleasure cruises and even if Cortez gave his ship to Flavio for awhile, it would be of no avail because the ship was bound by magical force; it can no longer move without the Skull Gem.
Flavio, knowing what Cortez was speaking of, pulls out his family's heirloom, the Skull Gem, the crucial object needed to allow the Black Skull to sail upon the ocean once more. Cortez is naturally taken by surprise that Flavio has the item in question. After Flavio willingly barters his valued possession that had been passed down to him from his family in exchange for usage of the Black Skull, Flavio earns Cortez's ire because Flavio's ancestors had stolen the Skull Gem from Cortez and says that Flavio must be either very brave or absolutely foolish to ask for such a request, and threatens Flavio by "turning him into a pinata and throwing a party on the beach". Flavio warns the deceased Pirate King that if Mario had beaten up Cortez once before, he'll have Mario beat him again and whilst fighting, Flavio would throw the Skull Gem into the ocean so it may never be found. Grudgingly, Cortez takes the Skull Gem, confessing that he was sick of hearing the X-Nauts' cannons blasting outside anyway, and Flavio comments that he never made his fortune by failing to strike a hard bargain, and then Cortez prepares for sailing across the ocean once more. Cortez's Ember minions then appear at his call, and Mario alongside the entire crew get ready to take the fight to Lord Crump.
After an all-out brawl, the X-Nauts against the crewmen and the Embers, and Mario against Lord Crump, they achieve victory and Lord Crump is forced to retreat.
Apparently, after the incident and bidding Mario farewell for now, he got insurance for his boat wreck and became the second richest man in Rogueport.
Flavio was punched in the face by Zess T. after causing gourmet ingredients to spoil on the dock by holding up a crew with a two-day story. He temporarily lost his memory as a result.
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