What is the name of the secret final boss in Kirby Triple Deluxe?

The secret final boss in Kirby: Triple Deluxe is Soul of Sectonia. She appears at the end of The True Arena, an optional boss-rush mode unlocked after completing the main adventure.

Soul of Sectonia is a more powerful version of Queen Sectonia, the main story’s final villain. In the story, Sectonia merges with the Dreamstalk and becomes a gigantic flower-like creature threatening Planet Popstar. After Kirby defeats her, the True Arena reveals that she can be revived using Miracle Fruits, leading to the bonus battle.

The fight is more than a simple rematch: Soul of Sectonia uses new attacks and patterns, including several visual and mechanical references to earlier Kirby “Soul” bosses such as Marx Soul and Drawcia Soul. The name can be confused with Queen Sectonia because both refer to the same central antagonist, but “Soul of Sectonia” is the distinct optional boss designation.