Kracko is the boss found in Mustard Mountain.

Stone

Start the fight by flying above Kracko. The moment Kracko's health becomes full, puff and then attack. If timed correctly, Kracko should take 2 hits.

During the fight, it is possible to land 3 hits from the top, or 2 hits from the bottom, if you attack perfectly in sync with Kracko's bobbing. The 2 bottom hits can theoretically be used to defeat Kracko even faster than the other methods, however actually landing those attacks is very difficult.

Left Side

Left side is the most common way of fighting Kracko. Wait for Kracko to attack before reacting. After avoiding the attack, float up and perform 2 sets of attacks for a total of 4 hits. Some attacks take longer and are more dangerous than others, so it takes patience and practice to dodge them.

Right Side

Right Side Fight  
 

The gif above demonstrates the riskiest Kracko pattern executed with this method.

Right side is an alternative, faster method of fighting Kracko. As long as you avoid getting hit, this method is far more consistent than the Left Side method since waiting isn't necessary. Immediately after landing the first hit, jump and float up to perform 2 more sets of attacks. If you're fast enough, you can avoid any attack Kracko performs and react from there.