Party member

Mario has had many partners during all his adventures, all of whom help him during many points of time. Mario 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." Luigi also gets partners in Paper Mario: The Thousand-Year Door, though the player cannot play as them, for Luigi is not a playable character in the game.

Mario & Luigi series partners

 * Mario
 * Luigi
 * Baby Mario
 * Baby Luigi
 * Stuffwell
 * Starlow
 * Bowser
 * Prince Dreambert
 * Paper Mario

Super Mario RPG: Legend of the Seven Stars partners

 * Mallow
 * Geno
 * Bowser
 * Princess Toadstool

Paper Mario partners

 * Goombario - The youngster from Goomba Village who travels with Mario.
 * Headbonk - Headbonks any ground or flying target (0 FP)
 * Tattle - Will analyze any enemy (discovering their HP and Defense), and will open text about the enemy (0 FP)
 * Charge - Increases next Turn's ATK by 2 (1 FP, Super Rank)
 * Multibonk - Headbonks any target on the ground or flying multiple times (3 FP, Ultra Rank)
 * Kooper - Joins Mario after he and Goombario recover his shell for him.
 * Shell Toss - Shoots Kooper's Shell at the closest ground enemy (0 FP)
 * Power Shell - Strikes all ground enemies with Kooper's Shell (3 FP)
 * Dizzy Shell - Makes all ground enemies dizzy (4 FP, Super Rank)
 * Fire Shell - Strikes all ground enemies with Kooper's Shell on fire (5 FP, Ultra Rank)
 * Bombette - After he frees her from the cage in Koopa Bros. Fortress, she joins Mario.
 * Body Slam - Body Slams the closest ground Enemy (0 FP)
 * Bomb - Bombs the closest ground enemy (3 FP)
 * Power Bomb - Bombs all ground enemies (6 FP, Super Rank)
 * Mega Bomb - Bombs all enemies (8 FP, Ultra Rank)
 * Parakarry - After Mario finds and returns some of the letters he's lost, Parakarry decides to ally with him and collect letters along the way.
 * Sky Dive - Parakarry, while airborne, kicks any enemy (0 FP)
 * Shell Shot - Parakarry, uses his shell for a more powerful attack against any enemy (3 FP)
 * Air Lift - Can lift any enemies out of Battle (3 FP, Super Rank)
 * Air Raid - Flies around at a hyper pace damaging all enemies (6 FP, Ultra Rank)
 * Lady Bow - Forces Mario to take a deal; if she and Mario defeat Tubba Blubba, she'll release the third Star Spirit, Skolar.
 * Smack - Hits any enemy 1-6 times for 1 damage each (0 FP)
 * Outta Sight - Makes Mario invisible, making him unable to take damage (skips Bow's next turn, 2 FP)
 * Spook - Scares enemies away (3 FP, Super Rank)
 * Fan Smack - Hits any enemy up to 5 times with more power than Smack (5 FP, Ultra Rank)
 * Watt - Joins Mario when he saves her from the Big Lantern Ghost.
 * Electro Dash - Attacks any enemy piercing Defense (0 FP)
 * Power Shock - Paralyzes any target enemy (2 FP)
 * Turbo Charge - Ups Mario's ATK by 1 for a # of turns (3 FP, Super Rank)
 * Mega Shock - Paralyzes all enemies (5 FP, Ultra Rank)
 * Sushie - Joins Mario after he saves her in the Jade Jungle.
 * Belly Flop - Jumps on any ground or flying enemy (0 FP)
 * Squirt - Shoots Water at any target (3 FP)
 * Water Block - Ups Mario's DEF by 1 for a # of turns (3 FP, Super Rank)
 * Tidal Wave - Throws a wave of water at all enemies (6 FP, Ultra Rank)
 * Lakilester - Former minion of Huff N. Puff, joins Mario after his girlfriend Lakilulu successfully convinces Mario to spare his life.
 * Spiny Flip - Throws Spiny Egg at any target. (0 FP)
 * Spiny Surge - Throws many Spiny Eggs at all enemies. (4 FP)
 * Cloud Nine - Gives Mario a chance to dodge an attack for a number of turns (4 FP, Super Rank).
 * Hurricane - Blows enemies out of Battle. (5 FP, Ultra Rank)

Paper Mario: The Thousand-Year Door partners

 * 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.
 * Headbonk - Headbonks any ground or flying target (0 FP)
 * Tattle - Will analyze any enemy (discovering their HP, Attack and Defense), and will open text about the enemy (0 FP)
 * Multibonk - Headbonks any target on the ground or flying multiple time (3 FP, Super Rank)
 * Rally Wink - Gives Mario another chance to act (4 FP, Ultra Rank)
 * Koops - Koops's father hadn't been seen since he'd gone off to challenge the ferocious dragon Hooktail. After hearing that Mario and Goombella planned to launch a fresh assault, he decided that he wanted to join them to prove to everyone (particularly his girlfriend Koopie Koo) that he could be tough like his dad.  Koops has a Defense of 1, but can be knocked on his back like enemy Koopas.  He has 10 HP initially, 15 at Super Rank, and 25 at Ultra Rank.
 * Shell Toss - Shoots Koops's Shell at the closest ground enemy (0 FP)
 * Power Shell - Strikes all ground enemies with Koops's Shell (3 FP)
 * Shell Shield - Provides a temporary shell to defend Mario (4 FP, Super Rank)
 * Shell Slam - Attacks all ground enemies and penetrate their defense (6 FP, Ultra Rank)
 * Flurrie - Madame Flurrie was a retired actress, just dreaming of coming out of retirement when Mario and friends asked for her help with a small task. She found their stories of adventure alluring, and decided that she would come with them to help as much as she could.  Flurrie has 15 HP initially, 25 at Super Rank, and 35 at Ultra Rank.
 * Body Slam - A heavy attack on any enemy (0 FP)
 * Gale Force - Attempts to blow all enemies out of battle (4 FP)
 * Lip Lock - Flurrie kisses any enemy, dealing damage that penetrates Defense and healing herself the same amount (3 FP, Super Rank)
 * Dodgy Fog - Makes Mario Dodgy for a few turns so that he may evade enemy attacks (4 FP, Ultra Rank)
 * Mini-Yoshi - This baby Yoshi hatches from an egg that Mario found outside the Glitz Pit. He could be any one of a variety of colors and the player can name him.  He has 10 HP initially, 20 at Super Rank, and 30 at Ultra Rank.
 * Ground Pound - Hits any ground or flying enemy repeatedly for 1 damage each hit (0 FP)
 * Gulp - Swallows an enemy then spits it at another, damaging both; this move was the only way to defeat the Armored Harriers (4 FP)
 * Mini-Egg - Deals relatively low damage, but hits multiple foes and can also shrink enemies to reduce their power (3 FP, Super Rank)
 * Stampede - Summons a Yoshi herd to attack all enemies; hits multiple times for 1 damage each (6 FP, Ultra Rank)
 * Vivian - Once a member of the villainous Shadow Sirens, Vivian decides that Mario is much more deserving of her help than her sister Beldam is. She has 15 HP initially, 20 at Super Rank, and 30 at Ultra Rank.
 * Shade Fist - Punches any enemy and also burns the target (0 FP)
 * Veil - Vivian and Mario disappear into the shadows and can't be hit by attacks (1 FP)
 * Fiery Jinx - Blasts all enemies with fire damage that penetrates Defense and leaves them burned (6 FP, Super Rank)
 * Infatuate - Confuses all enemies (4 FP, Ultra Rank)
 * Admiral Bobbery - Admiral Bobbery had refused to go out to sea after a tragedy in his past. Mario must learn his secret to convince him to serve as navigator on a journey to Keelhaul Key, and he joins Mario's party shortly after the ship's crash.  He has 20 HP initially, 30 at Super Rank, and 40 at Ultra Rank.
 * Bomb - Damages the closest ground enemy (0 FP)
 * Bomb Squad - Tosses three time bombs that explode later (3 FP)
 * Hold Fast - Damages enemies that attack Bobbery directly for a few turns (4 FP, Super Rank)
 * Bob-ombast - Deals serious damage to all enemies (9 FP, Ultra Rank)
 * Ms. Mowz (optional) - A dashing badge thief, Ms. Mowz and Mario cross paths a number of times before she asks him to find a badge for her. Unknown to him, it was a test of his abilities--and once he passes and proves himself to her, she'll join the party and lend her treasure-sniffing abilities to the heroes.  She has 15 HP initially, 20 at Super Rank, and 25 at Ultra Rank.
 * Love Slap - Damages the closest ground enemy, ignoring Defense (0 FP)
 * Kiss Thief - Steals the closest ground enemy's item or badge (2 FP)
 * Tease - Makes enemies Dizzy (3 FP, Super Rank)
 * Smooch - Heals Mario 10 HP (10 FP, Ultra Rank)

Super Luigi series partners

 * Blooey
 * Jerry
 * Torque
 * Hayzee
 * Screamy

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.
 * 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: Sticker Star partners

 * Kersti
 * A stack of Toads (temporary)
 * Green Toad (temporary)
 * Wiggler Segments (temporary)

Paper Mario: Color Splash partners

 * Huey
 * Legendary Captain (temporary)

Super Mario series partners

 * Luigi
 * Princess Peach
 * Toad
 * Yellow Toad
 * Blue Toad
 * Yoshi
 * Nabbit
 * Luma
 * Cappy

Trivia

 * Every female partner in Paper Mario: The Thousand-Year Door is charmed by and kisses Mario. In Paper Mario, Goombaria does the same.

Partner