Kagero Mansion (or "Heat Haze Mansion") was a proposed sub-game in Kirby Super Star, conceived by Masahiro Sakurai as a hybrid of puzzle and action games with horror elements. It was ultimately not included in the game.

Kagero Mansion was one of the eight main sub-games included in Kirby Super Star's proposal document written by Sakurai sometime around 1993, before work on the game had truly begun. Although it was apparently approved by HAL Laboratory, it never entered development due to a lack of time and resources while the company was making the other seven sub-games (Spring Breeze, Gourmet Race, Dyna Blade, The Great Cave Offensive, Revenge of Meta Knight, Milky Way Wishes, and The Arena). It was not added to Kirby Super Star Ultra, and it remains an unrealized idea, with no concept art or other materials from it known to exist. After being unknown to the public for over two decades, its existence was revealed by Sakurai in October 2017 during an official interview conducted in recognition of the release of the Super NES Classic Edition microconsole.

The planned story of Kagero Mansion would have involved Kirby exploring a horror-themed mansion while afflicted with a curse that sealed his mouth shut. Without the ability to Inhale enemies, Kirby would have needed to find alternate methods of gaining Copy Abilities, such as by absorbing the fire from a lit candle to get Fire. In his own words, Sakurai would have intended the experience to be "completely different from the usual Kirby game."

(Sounds like a Kirby based Luigi's Mansion to me for some reason)