Meta Knight and King Dedede
Dark Meta Knight and Shadow Dedede
Parallel Meta Knight and Parallel Dedede
Galacta Knight and... King D-Mind (I mean, they both appear in Super Kirby Clash and they both betray Parallel Nightmare the minute they're summoned so...)
Morpho Knight and... Masked Dedede?
Kirby's Dream Land: This doesn't count, since Meta Knight doesn't make an appearance til Adventure.
Kirby's Adventure: Meta Knight and King Dedede
Kirby's Dream Land 2: Dark Matter Swordsman and King Dedede
Kirby Super Star: Meta Knight and King Dedede
Kirby's Dream Land 3: Ado and King Dedede
Kirby 64: Adeleine and King Dedede
Kirby & The Amazing Mirror: Dark Meta Knight and Bonkers
Kirby: Squeak Squad: Meta Knight and King Dedede
Kirby Super Star Ultra: Meta Knight, Galacta Knight, King Dedede and Masked Dedede
Kirby's Epic Yarn: Meta Knight and King Dedede
Kirby's Return to Dream Land: Galacta Knight and Bonkers
Kirby: Triple Deluxe: Dark Meta Knight, Masked Dedede and Shadow Dedede
Kirby: Planet Robobot: Mecha Knight, Galacta Knight and Dedede Clone
Team Kirby Clash Deluxe: Gigant Edge and King D-Mind#
Kirby Star Allies: Meta Knight, Morpho Knight, Parallel Meta Knight, King Dedede and Parallel Dedede
Super Kirby Clash: Aeon Hero and King D-Mind
Kirby Fighters 2: Meta Knight and King Dedede
Think about it, they aren't canon because they didn't happened in reality. The Meta knightmare subgames are just Meta knight's dreams if Kirby's adventures but he in it and not Kirby. Dedede tour is Dedede's dream if he didn't get kidnapped and tried to find the culprit of the bean stalk and destroyed the true, true evil (the mirror). And you probably wondering about the Arena and true Arena. Well they are Kirby's dreams. That's why galacta knight keeps appearing in it, why it's not canon and why the EX bosses are fought by Kirby. The souls of the villians could be their actual souls haunting Kirby's dreams, or Kirby gets a fear of them.
This explains why galacta knight is still alive, Meta knight dreams about fighting the strongest warrior. Dedede dreams about meeting the mirror world because someone told him(and the reason why Shadow Dedede is evil because Meta knight most likely told him about dark meta knight.) This also explains why the soul bosses are like the EX bosses from the subgames but they are only fought by Kirby.
Please comment of there are any plot holes in this theory.
Basically gijinka galacta knight.