Culex in Super Mario RPG is among the most beloved boss encounters ever featured in a video game. So, it might surprise you that it’s an entirely optional battle that has secret criteria to unlock. How do you even get to Culex in Super Mario RPG.
The answer to that is both weird and expensive. But we can essentially boil it down to three steps: Buy the fireworks, get the Shiny Stone, and unlock the door.
How to get the Shiny Stone
The door to Culex is located in Monstro Town, an area that you don’t visit until late into the game. Their door is rather easy to spot since it’s this big metallic-looking beast set between the town’s normal wooden doors. It’s locked, however, which is what you need the Shiny Stone for.
You can get the Shiny Stone in Moleville immediately after freeing Dyna and Mite from the mountain. You can find it in the Pur-tend store. That’s the little mole hiding behind the row of boxes near the center of town. However, she’ll only give it up for some fireworks.
To get the fireworks, you need to buy them from the Mole in the house near the stairs to the mine. Conveniently, it’s located near the Pur-tend store. The Mole wears overalls and sits near boxes in the corner of the room. He’ll say he’s working on fireworks and will sell them to you for 500 coins.
Disturbingly, he says that the fireworks aren’t yet perfected, and your next task is to deliver them to a child. Luckily, Mario has no real morals, so you can easily swap out the incomplete explosives to the girl for a Shiny Stone.
Once you’ve doomed the little girl, you can take the Shiny Stone to Monstro town. If you interact with Culex’s door, it will say that the Shiny Stone is reacting, which will unlock the door. You then have one more opportunity to back out of the fight.
Which might be a good idea. If you walk into the Culex encounter like you have an appointment, you’re going to get whomped. It’s the most difficult boss encounter in the game, right next to the rematch against Culex.
Want a hint on how to beat them? Aim for the crystals to begin with. I’d recommend beginning by attacking the Red (fire) or Blue (water) crystals. Take them down as fast as possible because each crystal gets an attack, as well as Culex. This means, in the beginning, you’re dealing with five attacks each round.
However, I’d also suggest holding off on the fight against Culex, at least until you’ve obtained the Lazy Shell. Equip Mario with the weapon Lazy Shell and Peach with the armor. With this, Peach can concentrate on keeping the party healed, while Mario (and whoever else) can focus on damage.
As for the rematch against Culex, you don’t have to worry about that until the post-game.