Multiplayer (or n-player or nP, with n being any number greater than 1) refers to any game or Sub-Game which can be played by more than one player at a time. While most games in the Kirby series are primarily or solely single-player (and specifically designed as such), several allow for multiple players to varying degrees. Despite this, the only games in the series designed primarily for multiplayer gameplay are spin-off titles, such as Kirby Air Ride and Kirby's Dream Course.
Multiplayer by Title
The following lists multiplayer features in each game in the Kirby series in chronological order. Titles which bear no multiplayer at all are omitted from this list.
Kirby's Dream Course
In Kirby's Dream Course, a second player can take control of an opposing yellow Kirby (known as Keeby) to play in turns with the first, who controls Kirby. Gameplay revolves around who can get the best par on each course.
This clone of Puyo Puyo allows for a 2P mode, which is like the main game, but pits two players against each-other.
Kirby Super Star (Ultra)
This game introduced the Helper system, which allows Kirby to transform his currently equipped Copy Ability into a creature who would grant that ability when swallowed, who will then help Kirby fight. The Helper is controlled by the CPU by default, but if 2 Player mode is selected after the title screen, a second player can join in and control this Helper whenever it appears. The Helper has access to the full array of moves specific to its ability, and can also use an Infinity Jump to keep up with Kirby. It can engage in a Face-to-Face with Kirby to restore stamina, as well as picking up Food on its own. It cannot, however, cause the screen to scroll, and will be Space Jumped back to Kirby whenever it gets left behind, leaving de-facto focus on the first player still.
Kirby's Dream Land 3
At any point during gameplay, Kirby can call upon a partner named Gooey, who is controllable by a second player. Gooey, like Kirby, is able to fly, and copy abilities, though he does the latter by wrapping his tongue around enemies, rather than Inhaling them. While Gooey is out, Kirby has one less bar of stamina than he would otherwise.
Kirby 64: The Crystal Shards
Kirby: Nightmare in Dream Land
Kirby Air Ride
One of the few games in the series specifically designed for multiplayer, up to 4 players can take part in any of the main game modes. In all cases, Kirbys of varying hues compete against each-other to win races, or compete in the City Trial mode. Kirbys can attack each-other by doing Quick-Spins or by using Copy Abilities and other items which, depending on the settings, can destroy the vehicles of their opponents, or just slow them down.
Kirby & The Amazing Mirror
In this title, Kirby is split into 4 copies of himself, which all can be controlled autonomously by different players. Unlike in Super Star, Kirbys have free reign to wander wherever they like, as far away from each-other as they want to, and can regroup by using their Cell Phones to call each-other.
Kirby's Epic Yarn
Much like in Dream Land 3, a second player can jump in at any time as Prince Fluff to join Kirby in the Main Game. Fluff has exactly the same moves as Kirby. When certain Metamortex transformations occur, whichever character touched the item will become the primary controller, while the other takes a secondary role which cannot be used in single-player.
Kirby's Extra Epic Yarn does not feature multiplayer, relegating Prince Fluff to a secondary role.
Kirby's Return to Dream Land
Up to 4 players can join in at any point during the Main Game, and can choose between Meta Knight, King Dedede, Bandana Waddle Dee or a Kirby of a different color to play as. Joining in this way costs a 1-Up, but can still be done even if none are remaining. Each character has their own unique set of abilities, with Meta Knight being like a combination of Wing and Sword Kirby, King Dedede using the Hammer move-set, and Bandana Waddle Dee using the Spear move-set. Only a Kirby, however, can use the Super Abilities. Players 2-4 can be KO'd as many times as they want without interrupting the adventure, but if the first player controlling Kirby gets taken out, the adventure ends like it would in single-player mode. To help prevent this, the party can engage in Face-to-Face with each-other to share the Food they collect.
Kirby Fighters Deluxe
This expanded version of the original Sub-Game from Triple Deluxe allows up to 4 Kirbys to battle in a Super Smash Bros. like fighting game, but with a more traditional system of stamina. Players can fight in a free-for-all manner, or play in teams. To further distinguish each-other, unlockable costumes can be used for the various Copy Abilities.
Kirby and the Rainbow Curse
Up to three Bandana Waddle Dees of different hue can assist Kirby in the stages, by carrying him and dealing with enemies. The Bandana Waddle Dees are the only ones who can defeat the Grab Hands who appear in the stages.
Kirby: Planet Robobot
Team Kirby Clash Deluxe
Like the original Sub-Game, this title supports local multiplayer with up to 4 players. Using the local 'Wireless Quest' mode, a team of four can be established to take on a quest. All participants will be rewarded for a victory, but only the host player can satisfy Heroic Missions specific to the encounter.
Kirby Battle Royale
This action-multiplayer title is the first in the series to have full online matchmaking and a global ranking system. Up to four players can take part in battles, choosing between a handful of Kirby Copy Abilities, or as other characters to play as. Like with Kirby Fighters Deluxe alternate costumes can be unlocked for the copy abilities and other characters, some using amiibo.
Kirby Star Allies
This title marks the return of the Helper system, but instead of creating a Helper from a Copy Ability, Kirby befriends enemies directly from the field by tossing a heart at them. Up to 3 Helpers can be on the field at any one time and, like Kirby, can make use of the Power Combo system to enhance their attacks. Different color Kirbys do not feature in the Story Mode or extra games, but are playable in Chop Champs and Star Slam Heroes.
Super Kirby Clash
In addition to local multiplayer, the sequel of Team Kirby Clash Deluxe features full online multiplayer, and offers a large array of extra quests (called Party Quests) to play with others in. These quests are entirely separate from Story Quests, and have their own unique Heroic Missions to satisfy.
Kirby Fighters 2
This sequel to Kirby Fighters Deluxe has the same multiplayer features as its predecessor. It also allows for full online multiplayer in standard matches with up to four participants. In addition, Story Mode: The Destined Rivals allows a second player to join in.