Decided to make a gif showing my concept of what a true arena version of Kirby's Dreamland 3's Boss Butch would look like if the tradition of True Arena started here instead of Kirby Super Star Ultra.

Boss changes in order of being fought:

Whispy Woods EX: Phase one fights almost identical but he has the chance to spawn Gordos instead of fruits which can't be inhaled and he can shoot out 3 air puffs at once instead of one. Phase two can now stop to send out long spiked roots like in Kirby's Dreamland 2 and now has a chance to shoot a Gordo instead of a rotting fruit.

Blocky EX: Fights similarly to how his DX form fights in Triple Deluxe minus the attack where he goes into the background to grow himself to flatten Kirby

Boboo EX: Leaves a fiery trail during its charge attack which lingers for a bit and can shoot fireballs similar to Rick's own attack when using him with Burning

Captain Stitch EX: Floats faster after Kirby and now has the chance to fake out a charge if Kirby moves out of the way too early.

Acro EX: Phase 1 is slightly faster, but will switch to phase 2 after reduced to 75% HP instead of 50%. Arena is much wider which means more opportunities for Acro to attack before ramming into a wall.

Pon and Con EX: More Pon Jrs and Con Jrs appear and 2 spiked bombs drop instead of 1.

Haboki EX: Sweeping attack lasts twice as long and jumping attack now stuns Kirby if he's on the ground

Jumper Shoot EX: Jumping attack can now also stun Kirby similar to Haboki EX, and gains 2 new attacks. The first is short-ranged lick attack and the second is a rain attack where you must be under Jumper Shoot as it flies over raindrops.

Yuki EX: Throws snowballs much more frequently and can make icicles fall from the ceiling.

Adeleine EX: Her whole fight is changed and now summons 8 paint bosses instead of 4
Poppy Bros Sr: Fight like his Extra mode counterpart in Dreamland 1, but leaves a trail of explosives during his dash.
Bonkers: Moveset is identical to Kirby Super Star.
Dyna Blade: Identical to her fight in Super Star.
Kracko EX: The only boss from the original fight that is returning from the original fight, but now fights like Kracko's Revenge in Super Star Ultra.
Chameleo Arm: Fights like his counterpart in Super Star.
Meta Knight: Slashes at Kirby if he's close and charges at him with his sword. Can fly to divebomb Kirby with Galaxia
Nightmare: Starts in his true form and can only be damaged if his tornado-like core is hit like his real counterpart.
Marx: Fight is identical compared to Superstar, but lacks the black hole attack. After all of these bosses are defeated, Adeleine loses her cool and charges at Kirby, but will only get knocked out if Kirby slides into her. If Kirby does nothing, he'll be damaged and Adeleine keeps attacking.

King Dedede EX: Phase 1's attacks are much faster and Dedede spends less time not attacking. Phase 2's projectile attack now changes direction thrice before flying away. The chomping attack moves twice as fast. Now gains a new attack where he shoots a quick lightning projectile at Kirby like with Dark Matter's own lightning attack

Dark Matter EX: Has 2x HP. Starts out in his Swordsman form and can use the attacks from Dreamland 2. At half HP, DM turns into his true form and the fight is identical to the original fight, but the palpations on his body explode at the apex of their fly time and attacks come out faster.

Zero-Two (or Zero Soul if we're introducing the Soul Bosses here): Fight would be almost identical to Zero at first, but after Zero's red eye is destroyed, his gored body returns and mutates into Zero-Two. From there, the fight plays out like an almost replica of Zero Two's, but can now use its wings to swat at Kirby.

I do not own Kirby. The series belongs to Hal Labs and Nintendo.