Walkthrough for the quest Fists of Fury: Toussaint in The Witcher 3 Blood and Wine, including details about how to defeat Mancomb, Still Waters and Colossus, both by conventional means, and by taking advantage of each champion’s particular quirks.
You can start this quest by grabbing the Fisticuffs! notice from a Notice Board (the one near The Gran Palace signpost in Beauclair certainly has it) or by simply talking to the “Bookie” at any of the pugilist clubs in Beauclair. They’re easier to locate by just grabbing the notice, however.
If you played the main game, you should know how this works; there are three pugilists across Beauclair: Mancomb can be found to the south, near the Nilfgaardian Embassy signpost, Still Waters lurks near the eastern end of the city, while Colossus can be found northeast of the Coopers’ Gate signpost. Go to each location, talk to the Bookie, make your wager, then win the fist fight, which can be done with the good ol’ parry-and-riposte routine. These are fairly high-level fighters, however, so you do need to be wary of their quick jab attacks.
Mancomb is your standard opponent who seems more eager to engage in a battle of words than fists. While he’s easy enough to defeat in a standard boxing match, you don’t have to bother getting all bruised and sweaty if you’re willing to work your wits, instead. After he calls you an “inbred hound”, retort with “Hear how pathetic and stupid you sound?”, then continue the battle of taunts with “Think you’re confused - that sounds a lot like your sister.” and finally “Should’ve quit before we even began.” to humble Mancomb. Defeat your foe in a battle of words or fists - the reward is the same either way - and move on to the next champion.
Shellacking Still Waters
Still Waters is less interesting, gameplay-wise, as you’ve no choice but to win a standard fight against your masked, mute foe. After you’re victorious you’ll be treated to a bit of a revelation about your foe - if the sounds made during the fight itself didn’t give it away - which gives Geralt a fine opportunity to show off his progressive ideals. It’s the thirteenth century, after all!
The last foe, Colossus, is as big as his name implies, but he really prides himself on his speed. So confident is he that Geralt poses no threat that he’ll make a special wager; if you parry three of his attacks (not necessarily in a row) and refrain from counter-attacking, you’ll win. He’ll even double your wager if you manage it. Since it’s inconceivable that you’ve made it this far without learning how to parry foes during fist fights, this should, if anything, be an easier method of winning, but you can also opt for a normal fight instead. However you do it, best Colossus and you’ll have defeated all three champions and earned the right to face Toussaint’s champion. This ends the quest Fists of Fury: Toussaint and begins Raging Wolf.