Super Mario RPG secret boss location

Those looking for a challenge in Super Mario RPG will be happy to know that there is a both a secret boss and more challenging fights in the post-game after you defeat Smithy.

The secret boss from the original game, Culex, does indeed return for the Switch remake, and there’s another fight that’s even harder than him after that. We detail how to find Culex for the first time in Super Mario RPG, and how to take out the additional secret boss below.

[Ed. note: Spoilers for Super Mario RPG below.]

How to find Culex in Super Mario RPG

To take on Culex, you need the Shiny Stone and access to Monstro Town. If you haven’t hit Monstro Town yet, just keep trucking in the game’s story until you get there.

You can get the Shiny Stone from a little girl in Moleville. She’ll trade it to you for a firework — which you can buy for 500 coins from a mole inside the building next to the little girl. The young mole girl can be hard to spot, but she’s behind these boxes here:

Image: ArtePiazza/Nintendo via Polygon

Once you get the Shiny Stone, head to the darker set of doors in the middle of Monstro Town. You can insert the Shiny Stone into the door and enter, though before you do, prepare for a pretty tough fight against Culex, the Final Fantasy-inspired boss.

We had no problem beating Culex after we cleared the game, but fighting him earlier may pose a challenge.

Once you beat Culex, you’ll get the Quartz Charm, an accessory that halves the damage you receive and adds 50% more damage to your own attacks.

Once you beat the Smithy and Culex, you’ll be able to take on another secret boss, as part of post game content...

Graphic: Julia Lee/Polygon | Source image: ArtePiazza/Nintendo via Polygon

How to find post-game Culex in Super Mario RPG

After beating Smithy and Culex the first time, you’ll actually be able to rematch a harder version of Culex. However, to do this, you have to clear out the post-game, which means you need to complete all the available rematches:

• Jinx (in the Monstro Town dojo)
• Booster (in Booster Tower)
• Punchinello (in the Mole Mines)
• Johnny (in the Sunken Ship)
• Belome (in Belome’s Temple)
• Bundt (in the Marrymore chapel)

Along the way, you’ll get rewards like a weapon for Bowser or accessories that’ll make the other fights easier. Johnny specifically rewards you with the Extra-Shiny Stone, which you’ll need to open the door to Culex for this extra fight. However, Culex’s door in Monstro Town will not be there until you complete all rematches against the baddies above, based on our playthrough at least.

These fights are all tough and have new gimmicks added on top of the original fight, so don’t be surprised if it takes you a few tries to get through.

Once you actually get to the second Culex battle, prepare for the fight of your life. He’s significantly harder and beefier than the original Culex fight, so if you’ve been holding on to items like Rock Candy or Red Essence, now is the time to use them.

This version of Culex rewarded us with a key item that we haven’t quite figured out the use for. He also does count the number of turns it takes to beat him, so there’s no doubt that many experienced players will be racing to see who can take him down the fastest.

For more Super Mario RPG guides, check out our party member unlock guide, Melody Bay music puzzle guide, or our list of all the hidden treasure locations.