This page explains where to find the Sage of Marbule aboard the S.S. Zelbess in Chrono Cross: The Radical Dreamers Edition.
How to Lose Your Boat
After meeting Irenes in Marbule (Home World), return to your boat and sail towards the S.S. Zelbess, which is moored at the north-east side of the main island. This is the Home World counterpart of the S.S. Invincible.
Upon boarding the ship, head up to the main deck, then take the stairs towards the far right. On the upper floor, enter the captain’s cabin towards the far left, at the top. Irenes will briefly talk with Fargo, before leaving.
Now go down the ladder near the center to reach the lower floor. Take a right and enter the last door, just before the crew member blocking the way. If you met Irenes, there should be an old man sitting on the floor–this is the Sage of Marbule. Speak to him and he’ll leave the room, towards the area that’s blocked off.
Return to the captain’s cabin to try and get permission from Fargo to enter the blocked off area. He’ll challenge you to a game of roulette. Leave the cabin and enter the casino directly below. No matter how you play, you’ll lose the game–and access to your boat.
How to Become a Cat
Go back down to the lower floor and enter the inn towards the far left. The innkeeper will come down from a ladder and your party members become extremely suspicious, since the casino is directly below the inn…
Next, enter the door to the right of the middle ladder, still on this lower floor. Stand below the stage to watch Sneff’s magic trick. Then exit the room and repeat to see Sneff perform again (not necessary if you already saw the first trick beforehand). Hey, presto, you’ll become cats! Quickly escape the room.
While in cat form, go upstairs via the central ladder. Then enter the kitchen on the right, via the small cat-sized door. Speak to the cat inside to grab the Monster Mouth Frame. Also, open the chest near the back for a Frypan Ag47.
Okay, back to business. Go downstairs via the ladder and enter the inn. Crawl underneath the counter on the left and climb up the stairs. You’ll see the innkeeper rigging the game… Afterwards, go over to where the shiny handle is and pull it, to obtain the Handle.
Sadly, your days of being a cat are over (although in Lynx’s case, he’ll still be a big cat). Return to the room where the magic show was performed. Along the right wall, there’s another cat-sized gap that you can use to enter the backstage room. There, speak to Sneff to return to normal.
Everything is now in place. Head back upstairs and speak to Fargo in his cabin, to challenge him to another game. During this time, he’ll have a visitor in the form of Nikki. At the casino, without a way to rig the game, Fargo will always lose. You’ll get your boat back and access to the blocked off area.
Return downstairs and speak to the crew member towards the far right to continue further in.
Meanwhile, to progress the story, go through any of the three side doors below. Outside, the Sage will immediately return inside. Follow him back inside (again, via any door). Keep going in and out, until the Sage gives up. When prompted, choose violence.