In most Kirby games, Kirby will use a special weapon to defeat the final boss.
In Kirby's Adventure and Kirby: Nightmare in Dream Land every time you defeated a boss you would get a piece of the Star Rod. After you defeated King Dedede Kirby will place the finished Star Rod in the Fountain of Dreams while Dedede was pleading to get Kirby to stop his actions. Then Kirby springs into action with the Star Rod and blasts away at Nightmare.
Also, In Kirby: Squeak Squad, After defeating Daroach when he is possessed by Dark Nebula, You gain the Triple Star Rod, A weapon which is similar to the Star rod but it has 3 projectiles that come back to the rod, similar to a boomerang effect.
 The Star Chariot & Nova
In Kirby Super Star right before the final boss you fight Nova because since the sun and moon are fighting Marx can be grant a wish. (Milky Way Wishes) So Kirby is able to ride the Star Chariot and you will get to play a shoo-em up like game where you shoot everything in sight will the Star Chariot. If you want to play Co-Op you may if you want. Later in the Shoot-em up level where you need to fight the Heart of Nova which is destroying robotic power generators. After that you fight Marx.
 The Love-Love Stick and Zero
In Kirby's Dream Land 3 in every stage you are required to complete special missions to obtain a "Token of Love" after you collect one from every level you will get to fight Zero. He is fought like you fight Nightmare in his first stage.
 Crystal Shard Cannon & 0²
In Kirby 64: Crystal Shards if you collect all of the crystal shards scattered around the universe and get to 0² the power of Ribbon's flying ability and the crystal shards will give you the crystal shard cannon. You use it to shoot 0² in the eye and in his halo.