Main characters
Kirby
Kirby's the star of the game, having defeated Dark Matter once before. Kirby retains much of his standard techniques. His main form of attack is by inhaling enemies an objects. Once he has inhaled something, he can either spit it back out as a projectile or swallow it, instantly destroying the object or enemy. Kirby can inhale multiple enemies at once, which creates a more powerful projectile when he spits it out. Additionally, Kirby can damage most enemies by bumping to them from below, sliding at them or dropping on them after a long fall.
Kirby's most iconic technique is his copy abilities. When Kirby swallows certain enemies, he can gain a copy ability, which takes away his inhalation but lets him use an array of new attacks. These abilities range from projectiles that let Kirby chip away at enemies safely to turning Kirby into a ball of damage that defeats all nearby enemies. Finally, Kirby is also able to puff itself up, letting it jump in the air indefinitely. It will let out a puff of air when it exhales, which can also defeat minor enemies.
Gooey
Gooey is a piece of Dark Matter that has broken off from the main cloud and gained sentience. Unlike the entity it was spawned from, Gooey is quite naïve and simple-minded, posing no threat to the inhabitants of Dream Land. Gooey can be summoned by Kirby any time during a level by pressing 
, which costs one square or two units of Kirby's health. Kirby can still call out Gooey even if he has next to no health, and swallowing Gooey replenishes two units of health too, meaning that Gooey can be exploited to gain free health when you're almost dying.
Gooey possesses most of the abilities Kirby has. It can swallow and spit out enemies with its long tongue, as well as make use of copy abilities similar to Kirby. It also has infinite jumps. However, Gooey can't ride Animal Friends or swallow more than one object. Gooey can also instantly return to Kirby when he strays too far. When summoned, Gooey is mostly controlled by the game, and is often more of a nuisance than an assistant as it can steal enemies with copy abilities or destroy paths to certain secrets. However, Gooey can be controlled by a second player when an input is made on the Player Two controller. This is the only way to enable multiplayer play, but Player 1 can still inhale Gooey at any time to end the two player session.
Animal Friends
Along with our two heroes, there are plenty of allies that help out Kirby and Gooey on their adventure. The Animal Friend mechanic returns from the previous game as well as three of the original friends. Unlike their debut game, Animal Friends can be found in certain areas of the game, and Kirby can freely partner up, separate or switch Animal Friends. Each Animal Friend has their own quirks that either assist or impede, and each will alter Kirby's copy abilities in their own unique way.
Rick the Hamster
One of the three original Animal Friends, Rick is mostly grounded, and he excels on the ground. Rick's most useful ability is his wall jump, which lets him scale walls, and he also doesn't skid on ice. However, Rick can only jump once from the ground, forcing him to rely on his wall jump a lot. Rick is generally more useful in levels with a lot of ground and many enemies, as he struggles in difficult platforming sections.
Coo the Owl
Coo is part of the trio that assisted Kirby during his first bout against Dark Matter. Coo is a master at flight, being the only Animal Friend that retains Kirby's infinite aerial jumps. Coo offers much more control in the air, and can shoot forward in short bursts to fly against strong air currents that normally blow Kirby away. Relying on Coo's wings also means that Kirby can now use his inhale and copy abilities at any height. Coo suffers anywhere that lacks a lot of vertical space, but is overall an excellent partner.
Kine the Sunfish
Kine the Sunfish is the last of Kirby's returning allies, and it's in its element undewater. Kine offers better control while submerged compared to the normally cumbersome movement Kirby gets in the water. He can let Kirby inhale and swallow enemies underwater. He is also able to swim against strong currents that Kirby and other Animal Friends can't overcome. Kine is not very good on the ground, having only one jump and very slow movement out of the water. As underwater sections aren't very common, this limits Kine's use in many stages.
Nago the Cat
Nago, like Rick, is a ground specialist, although not as much as Rick. His most significant ability is his triple jump. Other than that and his versions of the copy abilities, there is not much else that he can boast.
Chuchu the Octopus
Chuchu is the token female of the group. While she is an aquatic creature like Kine, her exclusive techniques aren't too tied to the water. While she can help Kirby swallow enemies underwater, she also possesses multiple jumps and can cling to ceilings. Chuchu's method of grabbing enemies could take time to get used to, and can't grab multiple enemies at once, similar to Gooey's prehensile tongue.
Pitch the Bird
Pitch is the youngest of the six, and it isn't fully developed enough to have any of its own techniques. Its main draws are its alterations to Kirby's copy abilities, which aren't significantly better but quite interesting nonetheless. Pitch is also capable of multiple midair jumps, but can't fly infinitely like Coo.