How do you unlock the secret boss in Super Mario RPG?

Super Mario RPG is a stellar, faithful remake of the SNES classic game. You’ll see friends and foes alike loving recreated in 3D, but there’s one notable exception. It goes without saying that spoilers are down below.

When you get to Monstro Town in the remake, you’ll see a familiar locked black door. If you bring a Shiny Stone from Moleville to here, you’ll unlock a fight with the original super boss Culex. In the SNES game, this monster was very much in the style of the 16-bit Final Fantasy games, despite the pseudo-3D graphical style the rest of the game used. In the remake… he looks exactly the same.

You may, of course, notice some slightly different dialogue in this encounter. However, once you enter the new postgame of Super Mario RPG, you’ll unlock a series of boss rematches that put new twists on old foes. While most of these fights feature new mechanics to deal with, they generally look the same as they did before.

However, all that changes once you get to round two with our old friend Culex. Because he isn’t just Culex anymore. He’s now 3D Culex.

How do you fight 3D Culex in the Super Mario RPG remake?

To battle 3D Culex, you need the Extra-Shiny Stone item. You’ll earn this as a reward for the rematch against Jonathan Jones. While the black door normally disappears after you fight Culex, it will reappear in Monstro Town once you enter the postgame. Simply walk to the door with the Extra-Shiny Stone in hand and the fight will begin.

How hard is 3D Culex?

3D Culex is the hardest fight in the Super Mario RPG remake. While the original encounter could test you, 3D Culex will use much stronger attacks that will punish you if you don’t have sufficient weapons and armor. You don’t need all the best equipment and max levels to win, but it certainly helps.

For this reason, I highly recommend completing all the other postgame boss rematches first. Each of these fights rewards your party with new ultimate weapons, which will give you a leg up against Culex. Meanwhile, the Lazy Shell weapon and armor will come in clutch, giving Mario a hefty attack boost and another party member heavily fortified defenses. The Super Suit that comes from completing 100 Super Jumps in a row will also, of course, help a lot. However, if that challenge proves too tough, you can certainly beat the fight without it.

Best of luck in your duel against 3D Culex!