ソウルオブニル
The "Essence of Chaos", [[Void Termina]]'s core.

The boss that takes this name in particular is exclusive of the Soul Melter difficulty in [[Kirby: Star Allies|"The Ultimate Choice"]], replacing a nameless version of Void Termina's core from the main story.

Void Soul themself is also replaced in [spoilers]Soul Melter EX (the highest difficulty) by [[Void (Kirby)|]][/spoilers]
void soul