Kirby is an amoeba fact from ALivingWarCrime

He can freely have his limbs move all over his body, almost as if he had pseudopods like an amoeba. Not only that, but he can also freely change the shape of his entire body, like when he squats.

Not only that, but have you ever wondered how Kirby grabs things with no fingers? Kirby being an amoeba also explains why because Kirby could have selectively permeable membranes that can allow Kirby to grab things.

There is also one other small detail that also supports this, and that is his guard ability.

Now you may be wondering how an amoeba could guard itself from anything. Well, they can, by forming cysts, this hard thick layer of skin can protect the amoeba during extreme conditions.

But there's one thing that puts the nail on the coffin, and that is his copy ability.

His copy ability is directly related to endosymbiosis, something an amoeba and other cells do.

Endosymbiosis is where a cell eats another cell through endocytosis and the cell gains the ability of the other cell. For example, our mitochondria was once a cell on its own. But then our cell ate the mitochondria and gained its ability to make a ton of ATP.

Kirby does practically the same thing, where he eats an enemy (i.e. Waddle Doo) and gets the ability of the enemy (Beam).

And once he's done with the power, he goes through exocytosis where the ability leaves through a star.