Party member

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
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.
 * Goombella - An archeology student at the University of Goom, Goombella is searching for the same Legendary Treasure as Mario and decides that it is in their best interest to work together. Goombella has 10 HP initially, 20 at Super Rank, and 30 at Ultra Rank.

Characters

 * Mario - The first of the four Heroes of Light, Mario can Flip between dimensions.
 * Princess Peach - Joins Mario when she discovers she is a hero of Light. She can duck under her parasol, blocking most attacks, and she can also use it to float through the air.
 * Bowser - Joins Mario when he is convinced by Peach. He has twice the Attack of Mario, Peach & Luigi and can breathe fire, but he is larger and slower than the others and can't jump as high. He is also unable to climb ladders.
 * Luigi - Joins Mario when found in The Underwhere; can jump the highest of all the heroes and can also use his super jump technique to jump even higher and to deal double damage.

Pixls

 * Tippi - Allows the player to Tattle enemies and reveal invisible objects.
 * Thoreau - Allows the player to pick up and throw enemies and objects, as well as activate switches.
 * Boomer - Acts as an explosive.
 * Slim - Allows the player to turn sideways to move through narrow spaces and evade attacks.
 * Thudley - Allows the player to perform a Ground Pound.
 * Carrie - Can carry the player on a floating platform, allowing them to move faster, bypass spiky floors, and jump on spiked enemies.
 * Fleep - Can flip sections of the background, as well as enemies to make them briefly dizzy.
 * Cudge - Acts as a Hammer.
 * Dottie - Can shrink the player, allowing them to avoid detection by enemies and fit through small doors, pipes, and passages.
 * Barry (Optional - Unlocked by completing Chapter 3 and returning to the start of it and speaking to him) - Projects a barrier around the player.
 * Dashell (Optional - Unlocked by completing Flipside Pit of 100 Trials) - Increases the characters' speeds.
 * Piccolo (Optional - See Piccolo for unlocking instructions; a long list of errands) - Can use music to heal status ailments.
 * Tiptron (Optional - Sold by Francis after Chapter 8's completion for 999 coins) - Replaces Tippi after beating the game.

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.

Battle allies

 * Bob-omb
 * Spike
 * Bone Goomba
 * Professor Toad
 * Kamek
 * Bowser Jr.
 * Bowser

Mario & Luigi series

 * Mario
 * Luigi
 * Baby Mario
 * Baby Luigi
 * Bowser
 * Popple (during one fight with Wiggler)
 * Prince Dreambert
 * Paper Mario
 * Nabbit (during some fights in the Bad Nabbit mission)

Trivia

 * Luigi also gets partners in Paper Mario: The Thousand-Year Door: Blooey, Jerry, Torque, Hayzee, and Screamy. However, the player cannot play as them, for Luigi is not a playable character in the game.