What is the secret of paper mario

Answer from: Power Pikachu
A demon but i maybe wrong.

Answer from: Power Pikachu
The shadow palace is beyond the door, but at the end lies the demon's tomb. tell me if you want to know the treasure.

Answer from: superduperultra
Spoilers: At the end of the thousand year door there is a 1,000 year old demon. It is the 2nd hardest boss in the game. The demon takes control of princess peach. She has 200 hp. When you get to about 100 hp left she will show her true form and no attacks will work. None. After that the crystal stars will go to each of the seven areas and everyone will give mario confidence and the shelid will be broken. Then the real fight begins. Here are the attacks she has.

Slap - 6-7
HP Take - 6-8
Dead hand rush - 1-3 for each hit
Dead hand capture - 2-3 for each hit
Breath - Posion, Confusion, ultra Attack - She will charge Attack up 7. If you don't use Vivians Veil attack, it will deal 14 or more damage. You can superdodge it though, but it's EXTREAMLY hard. As soon as the dark ring hits the third candel, press B (and pray)

I'm not going to spoil the ending though. Only if you tell me pretty please with a cherry on top. (Okay not really)