Super Mario 64 DS

Well his panting is in the Haunted Hunt and it is where you have to get close to that boo but don't go out the door. You will then see his panting.

To see big boo outside you will need 15 stars deafeat the big boo to unlock Big Boo's Haunt. clear misson #1 on misson #2 get the luigi cap from a boo and then run back to the room and climb the stairs then go to the right enter that door jump on the platform and then backflip enter the door and jump into luigi's painting on the touch screen go the routes in order right up right I don't know 4th one maybe left if not then up run fast to avoid falling then jump on all of the moving Platfroms and enter the hole then deafeat King boo like a normal boo but you need to punch him 3 timesand then get Luigis key.

/\ And also you can even punch him even in the mirror or out of the mirror

You know the hallway where you see a boo and you follow it to the back of the castle? ok, do that then, as Mario, punch/Ground Pound the boo and there will be a cage. Jump into it and look for all the boos in the level and beat them. Then beat the Big Boo and there will now be a staircase whenever you go to the level. Get the star and come back to the level. Go upstairs, and to the very left end door. Grab the power flower and float to the upward platform and through the door. Go through the painting. Then go to the right door, then the left, right door, left, then go infront of the mirror, bossfight enjoy.

In the back of the castle through the door the is wooden and sticks out from the side go into the castle witch is found by ground pounding or sneak attacking the biggest boo then go into the door all the way on the left of the inside castle and got up on the box and jump onto the ledge go into the door and once the door opens you will see luigis picture then go in andThen go to the right door, then the left, right door, left, then go infront of the mirror, there will be the boss

You need to go in Big Boo's Haunt, NOT THE PICTURE IN THE ROOM WITH THE BIG MIRROR! In the main floor of the castle, go through one of the brown doors and follow the boo to the backyard of the castle. Find the big boo to the left of the backyard and ground pound him revealing a small thing. Touch it and you will go to Big Boo's Haunt. Go inside the haunted house and go upstairs. Go through the door on the far right. Using Mario, get the Flower Power from the ! block and float up. You should see a platform above you and a door. Press Z to ditch the Power Flower and go through the door. Then, WOOHOO, IT'S LUIGI'S PICTURE! Go in it to begin your quest to save Luigi. Here you fight King Boo but to get to him you must go throught the correct doors in every room. To help you, go through the right door, then left, then right again, then left again. Big Boo will stop laughing and ahead is a pathway. Run across the falling bricks and get on the moving platforms to get to the top. Then go into the hole and go up to the mirror. Keep moving until you stop and Luigi appears in the mirror in front of you. Big Boo appears and you fight him. Ground pound him in the mirror and on your side. You must get him on his shadow or in his normal form when he is on your side of the mirror. When you ground pound him three times, he is defeated and he will give you Luigi's key. Go to the room where you change characters and go to Luigi's door. Finally, you've unlocked Luigi! Hope this helps!

Just go to the boo place and then finish the big boos hunt and your done you get the key woo hoo