Mysterious Sir

The Mysterious Sir is a Raid Boss Heartless that appears in Kingdom Hearts Union χ during the  collaboration event in 2018. It is based on Kefka from Final Fantasy VI, particularly his final boss form from the same game. His battle theme from Final Fantasy VI plays while fighting it.

Design
The Mysterious Sir's appearance is heavily inspired by 's final form from . It has a violet muscular humanoid body, with clawed hands and feet and the Heartless insignia on its chest. In terms of attire, it wears a salmon-colored kilt that is tattered and has golden lightning-shaped markings, as well as a ring on its right hand and twin silver and gold wings on its back. Its face bears a strong resemblance to Kefka's, being a pale grey with a pink mouth, yellow eyes with black sclera, and yellow hair akin to Kefka's, as well as a white and pink band that extends beyond the back of its head.

The Heartless is accompanied by three Gummi Copter-like Heartless inspired by the :, , and. The Demon-based Heartless has a red color scheme, with a bronze wind-up and base. It bears the Heartless emblem on its front and has a horn pointing forwards, as well as two pairs of spikes jutting behind on both its right and left. The Goddess-based Heartless is blue with an elephant-like trunk, as well as a pink tail and bronze wings and tusks resembling Goddess's. The Fiend-based Heartless is navy-blue and sports an ivory mouth and copper horns and wings.