PP is used for casting PSI spells. Each spell uses a certain amount of PP, and if the amount of PP a character has fulfills that amount, then the spell is cast. The highest amount of PP obtainable is 999, although that is only available through hacking.
 Amount of PP on characters
Each character that can use PSI comes with PP. Characters who don't have the ability for PSI have no PP. It just remains as zero, and can never be raised.
Some characters have high PP, even at low levels, such as Paula Polestar, or Kumatora. Some have low PP, such as Ness. Each character gains PP as they level up. Some characters have low PP at the highest level (although it is still statisfactory) and some have high PP at the highest level, which means they can use powerful PSI and lose barely any PP. PP stats are basically the same for any character, with little or no changes, even on different cartridges. For example, a Ness on one Mother 2 cartridge could have the exact same PP, or similar, to a Ness on another. PP is raised by leveling up.
 Raising lost PP
PP can be regained by eating magic or PSI food items. Examples include Magic Gelatin, Magic Truffle, and PSI Caramel. Each food item increases lost PP for use again. Finding these items, however, is difficult. There are a limited number of Magic food items throughout the games. They cannot be bought at stores, which makes finding them difficult, and makes one wanting to use them reluctant. You can however use Condiments to raise the potency of these Items, There is also a special trick concerning the Magic truffle.
 The Magic Truffle Trick (EarthBound Only)
Fill your inventory with condiments that match the Magic Truffle, And the Truffle itself. (Found in the Deep Darkness swamps) Give the truffle to yourself so it's in the very back of your inventory, Then go into battle and use it. You'll use up the condiment and recover PP, But it's STILL THERE! this only works during battles though, And it also works with the Rock candy, Doing this trick with the Rock candy will result in Gigantic HP/PP Boosts when leveling up, But be careful, When a stat reaches 255 and is raised by one more, It will become 0. Not good eh?