Final Weapons are weapons and abilities commonly obtained by Kirby during the games climax, intended to be used during the Final Boss fight. These are usually incredibly powerful and typically tied to the game's story in some way. Some of them require assembly before they can be used.
In the Games
Kirby obtains the seven pieces of the Star Rod, which had been broken by King Dedede and guarded by his strongest minions across Dream Land. By gathering them together he is able to repair the Star Rod, and use the power of the Fountain of Dreams to defeat Nightmare.
By gathering the Rainbow Drops from the Rainbow Islands, Kirby can form the Rainbow Sword to combat the Dark Matter that has possessed King Dedede at Dark Castle. Afterwards Kirby uses the Rainbow Sword to repair the rainbow bridges connecting the islands.
Using the power of the Heart Stars given in gratitude by the inhabitants of Planet Popstar, Kirby forms the Love-Love Stick. Using this weapon, he once again battles the Dark Matter and eventually fights it's core 0.
If all of the Crystal Shards have been found, they form into the fairies' sacred Crystal, which then transforms into a powerful crystal shooting gun. With Ribbon's help, Kirby flies to the skies of Dark Star to face 02.
During the first phase of battling Magolor, Kirby has to use three of the Super Abilities in order to counter Magolor. Kirby finally finishes him off with the Ultra Sword, first using it to break the final part of Magolor's barrier, and then landing multiple deadly slashes on him, before drastically increasing the Ultra Sword's size, and ending Magolor's first form with a powerful slash.
During the final battle with Queen Sectonia during Story Mode, she possesses the Dreamstalk, fusing with it and taking over it's power. King Dedede and Taranza are able find one remaining Miracle Fruit and Kirby uses it to activate his Hypernova ability. With the Hypernova, Kirby is able to counter all of Queen Sectonia's attacks, spitting the flower buds at others to break Sectonia's barrier, and to inhale Queen Sectonia's laser and spit it back at her.
After Star Dream possesses President Haltmann's body and mind then takes off, Susie summons an Invader Armor for Kirby to use. As Kirby gets in and turns it into his Robobot Armor, Meta Knight shows up along with his Halberd. Kirby uses the Robobot's copy beam to fuse the Robobot Armor with the Halberd becoming Halberd Mode, which Kirby and Meta Knight both pilot during the final battle with Star Dream.