To defeat King Boo in Luigi’s Mansion 2, follow these detailed steps:

### Phase One: The Boxing Ring

1. **Initial Setup**:
– You will find yourself in a large boxing ring with King Boo.
– King Boo will lift up and slam himself back down on the arena, creating shockwaves that can knock you off balance.

2. **Luring King Boo**:
– While King Boo is following you around the arena, lure him to one of the shadows of the spikey balls.
– Shine your Poltergust in his eyes to freeze him in place.

3. **Wrangling King Boo**:
– Wait for one of the spikey balls to land on his head. This disorientates him for a second, giving you a chance to flash and wrangle him.
– Be cautious of the rolling balls; they can damage you if you make contact with them.

4. **Dodging Obstacles**:
– If you get hit by a ball, you will release King Boo. To avoid this, make sure to dodge the balls.
– If you get hit, you will have to start over from the beginning of the phase.

5. **Charging the Poltergust**:
– Charge the Poltergust to its max and press A to move on to the next phase. This helps in maintaining control over King Boo and avoiding obstacles.

6. **Transitioning to the Hallway**:
– The boxing ring will lift up, sending you hurtling into a large hallway filled with obstacles.
– Your mission here is to jump, dodge, and run through the obstacles until you reach the end of the hallway.

7. **Reaching the End of the Hallway**:
– Keep looking ahead and don’t stop running until you reach the end of the hallway and find yourself back in the ring.

### Phase Two: Lightning Waves

1. **Lightning Waves**:
– In this phase, you will find yourself back in the ring with King Boo.
– The round begins with him releasing waves of lightning over the battlefield.
– The tiles that are in the firing line will start glowing. Move to a dark tile to avoid the lightning strikes.

2. **Avoiding Hazards**:
– You will also have to contend with ice and sand-covered tiles that make movement even more difficult in the ring.
– Move carefully to avoid these hazards while King Boo is re-entering the ring.

3. **Luring King Boo Again**:
– Repeat the process of luring King Boo underneath one of the spikey balls.
– This will send you back into the hallway once again.

4. **Navigating the Hallway Again**:
– Make your way over and around the obstacles in the hall to begin the third phase.

### Phase Three: Increased Hazards

1. **Increased Hazards**:
– For the third and final phase, King Boo summons more lightning and more hazards in the form of spiked tiles in the arena.
– This makes wrangling him even more difficult than before, but follow the same process.

2. **Wrangling King Boo Again**:
– Lure King Boo underneath one of the spikey balls and wait for it to land on his head.
– This disorientates him, giving you a chance to flash and wrangle him.

3. **Final Battle**:
– Continue dodging obstacles and avoiding hazards while maintaining control over King Boo.
– With enough patience, you will whittle his HP down to zero.

4. **Victory**:
– When King Boo’s HP reaches zero, it stays that way for good, and you will have successfully completed Luigi’s Mansion 2.

By following these steps meticulously, you should be able to defeat King Boo in Luigi’s Mansion 2.