King Flyleaf's overall appearance resembles a Venus Flytrap plant while his hands resemble pitcher plants. He has a green head with red spots while his pitcher plant hands are yellow. The main head has a crown-like leaf formation on its head. King Flyleaf's lower body is stuck in a brown plant pot that has green tentacles sprouting from it. All heads don't have eyes while the main head has a sharp set of teeth.
In his EX appearance, King Flyleaf gains a larger crown formation while his pitcher plant hands gain a small crown-like leaf formation as well. He becomes a purplish color instead of his normal colors. On this appearance, there is also a cape made of leafs on its back. On the second phase of the battle, King Flyleaf is a lot bigger and taller physically. His hands turn into miniature Flyleaf heads instead of the original pitcher plant ones. He does not reside in a bucket but his lower body consists of a few tentacle-like spiny vines.
Kirby and his friends enter through a door which leads them to a lair filled with vines. A Fire copy ability pedestal appears here which lets Kirby get the Fire ability. Use the ability to burn the vines which will get startled and retreat. Once the 5 vines are gone, the torches light up which reveal King Flyleaf who will roar at the sight of Kirby and his friends, starting the battle.
King Flyleaf will stay in the far front of the stage and will shoot poisonous blobs into the ground, make his pitcher plant hands slam the ground, let his vines tunnel underground which will make several small vines appear on the stage whipping, bite the stage himself (which will create stars to throw at him), throw blade-like leaves or throw explosive seeds at the ground. To defeat him, wait until he slams to ground and attack him when he's stunned. Once defeated, the plant king's bucket will break and proceeds to fall into the dark abyss beneath.
A stronger and more powerful version of King Flyleaf appears in the game's EX mode, called King Flyleaf EX. This version can throw 4 blade leaves, throw 5 poisonous puddles and throw more explosive seeds. He's also much more faster. When defeated, he'll once again fall to the abyss beneath him, which will grant Kirby and his friends access to a part of the Fairy Queen's wand. The heroes will take their Warp-Stars and fly out of the cave where the boss was fought. While flying through the jungle, they'll notice the jungle being in flames. Kirby and his friends will get attacked by large Flyleaf plants on their flight and will also be blasted by poisonous blobs. After some time, King Flyleaf will appear in a huge form and will roar loudly, making the screen vibrate in the process. This form of Flyleaf has to be combatted using the Warp-Star. One has to shoot stars at the boss' mouth to defeat it. The boss will shoot poisonous blobs, seeds, make his newly Flyleaf-head hands bite the area, use his vines to make large sprouts out of the ground or the boss himself biting forward. Once defeated, the boss will roar one last time and plummet into the ground in defeat.
- The boss resembles the Piranha Plant enemies from the Mario series.
- It may also be a reference to Petey Piranha, a Piranha Plant boss from the Mario series.
- King Flyleaf bears a resemblance to the monster from Little Shop of Horrors, Audrey II.
- It also somewhat resembles Biollante from the Godzilla series.