Go up the stairs and collect the crystals along the way. Avoid the swinging spiky balls. Once at the top, climb the pillar on the right, which will move and lead you to the door. Go in.
Get on the pillar in front of you, which will move and lead you to another pillar. Get off quickly, as once you reach your destination, the pillar will shrink quickly. Grab the crystal and advance to the next pillar, which will move as well. It is nothing complicated, but you will have to watch out for the attacks of the two Dark Dantini on the wooden walkways on the sides. Don't waste time trying to reach them, just avoid them. Try not to get hit, to reach the boss with as many crystals as possible. Repeat the process until you reach the door. Enter to finally face your rival.
You will have to defeat Baron Dante three times to permanently eliminate him and each time he will attack you in a different way. At first, he will just chase you, and then violently punch the floor when you are close. Jump promptly to avoid the shock wave that will spread throughout the room. After missing you, Baron Dante will take his head in his hands. Quickly hit him with the tail or with a stomp attack. Repeat the operation two more times to conclude the first phase.
In the second phase of the fight, Baron Dante will position himself in the center of the room, always looking in your direction. If you stand still for a few moments, he will charge you, coming quickly towards you. Move quickly to avoid him. When the boss crashes into the wall, hit him quickly. Repeat the process two more times to emerge victorious from the second step as well.
In the last phase of the battle, Baron Dante will float in the center of the room, throwing lightning bolts at you. You will have to keep moving to avoid his attacks. After 3 lightning strikes, he will drop to the ground. Quickly reach him and hit him with the tail. You will have to repeat the process two more times to finally defeat Baron Dante. The second time, however, the boss will throw 6 lightning bolts at you before landing and 9 the third. On the third hit, you will kill him.
After defeating the boss, you will see the final cutscene of the game and the credits. At the end of the credits, however, if you have found all the Gobbos and collected the first seven pieces of the puzzle, you will be given the opportunity to restart the game from level 4-S2.