Culex, Dark Knight of Vanda · Super Mario RPG: Legend of the Seven Stars · Super Nintendo · 1996 · Optional Superboss
Behind a sealed door in a quiet town in a Mario game, Square hid a boss that was not a Mario boss at all — a 2D sprite from another franchise entirely, guarding four elemental crystals and set to a battle theme lifted from Final Fantasy IV.
Super Mario RPG: Legend of the Seven Stars was Square's one collaboration with Nintendo before the two companies parted ways over the Nintendo 64's cartridge format, and Culex is the moment the game quietly admits who made it. To reach him, the player must find a shiny stone in Moleville and use it to open a sealed door in Monstro Town — an entirely optional detour the main quest never mentions. Behind the door, in a void of purple-blue space, waits Culex: a self-described "Dark Knight of Vanda" who has nothing to do with Bowser, Smithy, or anything else in the game's plot. The most striking thing about him is visual. The entire game is rendered in Square's pre-rendered, Donkey Kong Country-style 3D sprites. Culex is drawn as a flat, deliberately old-fashioned 2D sprite in the style of a Super Famicom-era Final Fantasy boss — a visitor from another kind of game who does not match the world he has appeared in. He is flanked by four crystals, each governing a single element, exactly as the elemental Fiends of the Final Fantasy series had been. Mechanically he is the game's superboss, tougher than Smithy, the actual final antagonist. The crystals attack independently and must be managed while Culex himself deals heavy elemental damage, and the fight rewards preparation and knowledge of the game's systems rather than the level the main story leaves the player at. The music seals the tribute: the battle plays a reinterpreted version of a boss theme from Final Fantasy IV, and when Culex falls, the game plays the Final Fantasy victory fanfare, followed by the series' gentle "Prelude" crystal theme as Culex and Mario share a few quiet words. Culex endures because he is a piece of authorship smuggled into a licensed crossover. A player who had never touched a Final Fantasy game could beat him and simply think he was a strange hidden boss; a player who knew Square's work recognised every element — the sprite style, the crystals, the fanfare — as a signature. He is one of the earliest and fondest examples of a developer signing its work through an optional secret, and the fondness only grew when Culex returned, decades later, in the 2023 Super Mario RPG remake.
Super Mario RPG was made by Square on Nintendo hardware, and Culex is where that authorship becomes visible. Nothing in the main quest points to him. The player has to notice a shiny stone in Moleville, carry it to a sealed door in Monstro Town, and choose to open it — a sequence the game never requires or rewards in the story. What waits behind the door belongs to no part of the plot: a boss who introduces himself as the Dark Knight of Vanda and admits he has been pulled into this world from another dimension, which is very nearly a literal description of what Square did by putting a Final Fantasy boss in a Mario game.
Culex predates the era when franchise crossovers became routine marketing events. In 1996 he was an in-joke — a reward for the player who both explored thoroughly and recognised the visual and musical language of Square's other series. The flat sprite among 3D models, the four elemental crystals echoing Final Fantasy's Fiends, and above all the FFIV battle music and victory fanfare, added up to a private message from the developers to the players who would understand it. When Square and Nintendo went their separate ways shortly afterward, Culex became a small monument to the one time they had worked together — which is why his return in the 2023 remake was treated as an event in itself.