Party members, also known as partners or allies, are characters that travel with and battle alongside the protagonist in RPGs. The protagonist and his partners as a group are generally referred to as a party, as the event of a character joining is referred to as said character "joining your party."
Super Mario RPG: Legend of the Seven Stars
In Super Mario RPG: Legend of the Seven Stars, Mario's party eventually gains five members (including Mario himself), but only three of them can be active at any given time, and Mario must always occupy the first slot. Inactive party members still gain experience and level up after battles.
Paper Mario series
In Paper Mario for the Nintendo 64, partners are either referred to as Party Members or Mario's Friends. In this game, Mario can only have one Party Member active at a time. Switching Party Members mid-battle uses up Mario's turn unless he is wearing the Quick Change badge. Party Members do not have HP; most enemies' attacks will only target Mario, and the few that can hit Mario's Party Members will simply incapacitate them for a certain number of turns depending on how much damage they took. If the attack is successfully guarded against, the Party Member will take no damage. Party Members can be upgraded with Super Blocks, which increases their attack power and makes them learn new moves. Each Party Member can be upgraded twice, first to Super Rank, then to Ultra Rank. Mario must have the Ultra Stone to upgrade Party Members to Ultra Rank.
Paper Mario: The Thousand-Year Door
In Paper Mario: The Thousand-Year Door, Mario's party members are referred to as partners or allies. The party mechanics work similarly to the first Paper Mario, but with several changes. Partners now have HP and take damage the same way Mario does. Partners are now upgraded by giving Merlon three Shine Sprites.
Super Paper Mario
Paper Mario: The Origami King
In Paper Mario: The Origami King all party members are temporary, only accompanying Mario for specific periods of time or in specific streamer districts. Party members only have one attack in battle and are AI controlled.
Mario & Luigi series