to unlock waluigi do this
1)you must have all people
2)get mario
3)go in the cannon
4)shoot to the black box (I got a cool hack which allows you to see it)
5)when in it complete the level and beat the boss
6)blast to the peach painting
7)collect the upsidedown L key
8)go to the white room and this will take you to behind the door and you will not fall down
9)open the door with the key
10)enjoy waluigi!
You don't learn from success you learn from failure