The Sunken Ship is one of the longer dungeons you’ll face in Super Mario RPG, yet it only has one hidden treasure chest to uncover. It’s also fairly easy to (temporarily) lock yourself out of getting it.
To find the hidden treasure chest in the Sunken Ship, you want to enter this room where a clone of Mario appears. You’ll find this shortly after facing the King Calamari miniboss. Once you’re here, jump up near the center of the room on the side where the doors lead out. This will reveal a hidden J block, which will in turn reveal the hidden treasure chest. However, you’ll note it’s a little too high up to reach.
To get the real prize here, you’ll need to use the fake Mario as a platform. Do not talk to the other Mario, as this will trigger a battle and get rid of it altogether. This won’t lock you out of the hidden chest forever, but you will need to reenter the Sunken Ship to make fake Mario respawn. It’s easy to initiate that “Talk” prompt by mistake, so just avoid it.
You’ll have to finagle both the positions of you and your clone a bit to get the positioning just right. Clone Mario seems to have a problem multitasking, so goading it into walking and then jumping seems to make it not jump at the same time as you. Use this tactic to position yourself like in the screenshot above. You may need to flex the exact spot you’re standing in a bit if you can’t reach the chest. There’s no special trick to get extra height other than standing on Mario’s head, so just make sure you’re positioned just right.
Landing this treasure chest will net you a Flower. I hope that was worth the effort!
Check out where to find the other hidden treasure chests in Super Mario RPG here.