Like most of the Bosses found with the game outside of Madame Broode and Bowser, you will only face Knucklotec once during your journey. Good thing too, as he can be one of the more difficult to defeat among the rest (and so early in your adventure too). As the battle with Knucklotec commences, its head will summon two fists that will try to attack Mario, sending you on the run. As you run around, the goal is to stun Knucklotec by having one of said fists make contact with one of the number of ice patches on the ground.
Once stunned, Mario can capture Knucklotec's fist with the help of Cappy, allowing him to strike the monster smack dab in the face. This will send him into a fury, causing more ice blocks to be summoned. Do the same as before in order to stun Knucklotec, capturing one of his fists to attack his head for a second time. This time after doing so will result in Knucklotec hovering over the area. As he does this, he will shoot rocketing fists at Mario.
Simply dodge these fists as they come, causing Knucklotec to eventually return to the field of play. As he lands, even more ice will fall to the ground. As you dodge both the ice and his fists (this time trying to grab hold of Mario), do as before in order to stun Knucklotec. Capture one of his fists to attack him for a third time, and after you do, the match will end.