“I am matter... I am antimatter... I can see your past... I can see your future... I consume time... And I will consume you!”
Culex is an optional hidden boss who appears in Super Mario RPG: Legend of the Seven Stars. He is a Dark Knight from the alternate dimension of Vanda. Alongside the Elemental Crystals, Culex is an even more powerful boss than the main story's antagonist, Smithy. Culex's HP, combined with the HP of the Elemental Crystals, is 12,396.
Culex could be considered a crossover character from the Final Fantasy series, although he has never appeared in a Final Fantasy game. Nevertheless, the Dark Knight was designed as an allusion to the Final Fantasy series, as both Super Mario RPG: Legend of the Seven Stars and Final Fantasy were developed by Squaresoft.
Before or during the events of Super Mario RPG: Legend of the Seven Stars, Culex crosses over from the dimension of Vanda to Mario's dimension. Culex eventually comes to reside in a cross-dimensional region that is found behind a sealed door in Monstro Town, a village of reformed monsters, which is located in Land's End. Despite waiting in a dimensional rift, Culex's next-door neighbors can still hear the Dark Knight talking to himself through the walls. According to one of his neighbors, a Piranha Plant, Culex is "always mumbling about Crystal-this and an Evil-that."
The Dark Knight is sent to Mario's world to fight on behalf of the Dark Mage. However, Culex discovers that Mario's dimension was actually uninhabitable by himself and others of his kind. As such, Culex is forced to return to Vanda without completing the Dark Mage's assignment. Before he leaves for his home dimension though, Culex wishes to battle the worlds's "strongest knight."
The seal to Culex's dimensional vortex is eventually broken by Mario, the champion of the Mushroom Kingdom. Mario and his party discover the mysterious sealed door during their travels to Monstro Town. The Piranha Plant neighbor of Culex provides a clue to opening the sealed door, reporting to Mario about Culex's obsession with Crystals, and then hypothesizing: "Isn't a 'Crystal' some kind of a shiny rock...or something? I know I've seen those somewhere!" This "shiny rock" is actually a Shiny Stone, a micro-sized crystal that can be acquired in Moleville. To retrieve a Shiny Stone, Mario first must buy the Fireworks from a male mole in Moleville for five hundred coins, then trade the Fireworks for a Shiny Stone from a young mole girl in the same town.
Upon returning to Monstro Town with a Shiny Stone in his possession, Mario attempts to open the sealed door, causing the small crystal to begin reacting, eventually dispelling the magical seal. The door can now be opened, allowing Mario and company to access Culex in his dimensional vortex. After Mario enters the dimensional rift, Culex greets the visitors and explains his story. The Dark Knight then challenges Mario, who Culex views to have the potential to be the world's "strongest knight," to a battle before he had to leave for his home dimension of Vanda. The plumber can either accept or refuse Culex's offer. If Mario refuses, Culex says, "You are wise to hesitate. Without any weapon or armor, you have no chance." Mario is then forced to leave the dimensional rift, but can return as he desires at a later time. If Mario accepts the challenge, Culex declares "En garde!" and the battle begins.
In battle, Culex is aided by four seemingly sentient crystals – the Earth Crystal, the Fire Crystal, the Water Crystal, and the Wind Crystal. Each crystal has command over potent magic attacks aligned with their elemental power (for example, the Earth Crystal knows the special attack Boulder, which can damage Mario and both his allies in one strike). Culex himself is a powerful fighter, who has over 4,000 HP, the most of any character in the game besides the final form of the final boss Smithy. However, the group as a whole have over 12,000 HP, which is higher than that of both of Smithy's forms combined. The Dark Knight is also a master of advanced magic such as Shredder, Meteor Blast, Flame Stone, and Dark Star. All four Crystals can be defeated independently before targeting Culex, but if Culex is defeated, any remaining Crystals shatter one by one on their next turn.
If Mario is victorious against Culex and his four Crystals, the Dark Knight congratulates the world's "strongest knight." Culex is then able to return to Vanda satisfied, but before he departs, he tells Mario: "Thank you, brave knight. I will treasure this memento of my journey here. Perhaps in another time, another game, we may have been enemies... Let us part as comrades in arms." The Dark Knight then rewards Mario with the Quartz Charm, a special accessory that boosts attack and defense by 50% and also prevents instant death. Culex requests the plumber to "treasure it as a keepsake of their fight." Culex then leaves for Vanda, uttering the words "Farewell, champion knight!" Mario and company are transported back to Monstro Town and the door to Culex's dimensional rift disappears, leaving a solid rock wall in its place. Also when Culex is defeated, the Piranha Plant next door will comment that he thinks "our neighbor moved away".
 Allusions to Final Fantasy
As mentioned above, Culex stands out in the game Super Mario RPG: Legend of the Seven Stars for being an allusion to the conventions of the Final Fantasy series. Culex is described as being a Dark Knight, a common class of character from the Final Fantasy series. Furthermore, Culex's master, the Dark Mage, may be a reference to the Black Mage, another common class found throughout the series.
Also, Culex has two different sprites in the game, one for the overworld and a much larger one for battle, just like bosses in the Final Fantasy series. Super Mario RPG: Legend of the Seven Stars enemies (except for Valentina, Shelly, Jonathan Jones and Magikoopa), on the other hand, have the same sprite for both the overworld and for battles. Indeed, in the style of early Final Fantasy games, all enemies and bosses are rendered as static pieces of two-dimensional character artwork, lacking any kind of animation. Similarly, in battle Culex is rendered as a two-dimensional image that does not change when attacking or being attacked, unlike the three-dimensional models of all other enemies in Super Mario RPG, which can go through complex animations when attacking, being attacked, and even walking in place.
Additionally, Culex himself somewhat resembles the final form of Kefka, the final boss of Final Fantasy VI. Culex's battle music is the same as the Final Fantasy IV boss battle music (at the time of the game's release, the Final Fantasy II boss battle theme). Culex's name is also the Latin word for "Mosquito," which is a subtle reference to the main antagonist of Final Fantasy IV, Golbez, whose name is derived from a type of fly.
The four Elemental Crystals used by Culex in battle are also important reoccurring artifacts from the Final Fantasy series, appearing in many games in the series with different functions in each. All four Elemental Crystals featured in the battle are from the original Final Fantasy for the Nintendo Entertainment System.
Moreover, the three music tracks played when around Culex are remixes of three music tracks from the Final Fantasy series. His Battle Music is a remix of the Battle Music from Final Fantasy IV, the music that plays when Mario defeats Culex is a remix of the Victory Music present throughout the Final Fantasy series, and the Conversation with Culex is a remix of Final Fantasy's main theme. Lastly, Culex breaks the Fourth wall when telling Mario: "Perhaps in another time, another game, we may have been mortal enemies..." The Dark Knight is of course referring to his origin from the Final Fantasy series, versus Mario's place in the Mario series.
 Names in Other Languages