Right now I'm only at 97, I have all the cards, and found all the treasures, also some secret places. What's missing?
You don't have to buy all the items, that was never a requirement
I don't exactly remember the location of Oni/Noh mask. They are in some chest in the first area. One is in the past and one is in present.
To get te Plushie, chop down the bamboo in front of Rikku and then return her ball.