1, have alot of Mario Partys to use, spam Beanstar Blast for the fight against the bosses of the 100 trials, spam Maplo Cure for emergencies and have all the neccesary equipment for special attacks and defense (magical shirt, royal pants, cosmic mario pin, etc.).

Now finally, take notes to what i said about the magical shirt, royal pants, star piece items and star rank and ignore the rest of what i just said! The two most important facts to beat the pit of 100 trials are as follows.

Plus, you must, no matter what get another magical shirt for luigi (a shirt that is a rare drop for the golden blooper only, if you wish to know more about the golden blooper, speak up and i'll edit my post). Later, go to the beanbean kingdom to get the shop's special item, the royal pants (best pants for the bros in the game and of course, they come in pairs). The enemies over the 50th floor now come in large groups so have strong multi-targeting moves. After, go to the mushroom kingdom and (thoughtfully) waste your star pieces on attack, defense, hp and fp upgrades. Then, you get the buff badge as early as possible to strenghthen your stats. First, have all seven sages and have bowser's cosmic hammer + bullet bill shot (even though there are 2 instead of 1 boss, cosmic hammer is a strong single attack move). if you are lucky, you may be able to beat the pit of 100 trials with the right set-up at your level. actually it depends on how well you equipped rather than just how underleveled you are.But it is possible to beat the pit of 100 trials without star rank (for those who don't know, star rank is a way to reset your levels so you can get stronger).

Paper mario the pit of 100 trials