Alright, try one I went in after just beating the game with two ultra shakes. I got to room 61. Second time, I went prepared. I took six ultra shakes. My personal recommendation for those of you doing these; always use Peach/Boomer. The only case that I switch to Bowser is when fighting the large Easter Island heads mixed with trunk swinging elephant that take a bunch of hits. Anyway, even with the toughest of mobs you can just drop a bomb then duck with the parasol and blow up the bomb without standing. Very safe. In the whole ordeal I used a total of two ultra shakes plus what I picked up in the pit. Here is how it went.
Spoiler Alert!In room 100, you meet a voice that suggests it is friendly and all you have to do to prove yourself is do the whole pit a second time. Screw that right. Well a pipe comes out of the ground and when you go through the pipe...bam right back to the entrance of the pit. So, given my dedication to the cause, I went straight back in. Striaght though. The second time in room 100, you here the same voice, but this time it says that while it was created by the ancients it is not a friendly of them. Its name was Shadoo or something close to that. The actual boss fight consists of fighting a shadowed from of each of the four party members: Luigi, Bowser, Peach, and Mario respectively. The get access to the pixl's. Seriously though, with Peach's parasol and Boomer I got hit twice. Easy!
The treasure is: one normal card and one dark card for each of the four party members.
Kind of weak, but it felt good just beating it. Now back to the video store with it.