After reuniting with Edgar and getting rid of the tentacles in Figaro's engine room, you take the castle to Kohlingen.
145. Deep Eye
Go northwest from the castle to find Kohlingen. Go into the Inn/Cafe and talk to Setzer. He will join you. Equip him.
Go south and west from Kohlingen to find Daryl/Darryl/Darill's Tomb. Walk up to the mound, and Setzer will open it.
147. Osteosaur/Skeletal Horror
148. Mad Oscar/Malboro
Go south to the next area. Then go through the southwest door. Open the chest, then go downstairs and open the chest there. Before going through the door, walk through the wall on the right to find another chest. Then go back and go through the north door.
Go north and flip the switch, then go south, west up the stairs, and north. Go through the northeast door. Walk up to the grave and press A, then go through the door that opened, and go north and flip the switch.
Go south to the room with the grave, and go south again from there. Use the southeast door to find a chest. Then go north again. Go through the bottom-middle door. Press A to jump onto the turtle.
In the next room, flip the switch to raise the water level, then press A to jump onto the turtle.
In the next room, go north. You will see a save point. If you go northwest from the save point, you can open the chest to fight a Monster-in-a-box called Presenter/Presntr/Angler Whelk. If you defeat it, you get a Dragon Claw/Dragon Claws for Sabin.
Presenter/Presntr/Angler Whelk will die if either its head or its body dies (or both). If you can defeat both the head and body at the same time, you get two Dragon Claws. If you use Chainsaw on its head, there is a chance of killing it instantly. You can also use X-Zone/Banish for a chance to kill it instantly. Fire 2/Fira is effective against both its head and body.
After fighting Presenter/Presntr/Angler Whelk, or skipping it, go south from the save point, then go northeast to find another chest. This one just contains an item. From there, go north to the next room.
Go north and check on the purple altar in the center to fight Dullahan. Dullahan is weak to Fire. It can also be killed by reducing its MP to 0 with Rasp.
When Dullahan is gone, go north through the door that you just opened, and watch the cutscene, following Setzer and talking to him throughout the scene. Afterward, you will be over Maranda.
Be warned that when you fly around in the Airship, you will occasionally have random encounters with a boss called Doom Gaze/DethGaze/Deathgaze.
Sabin's Best Blitz
Now that you have the airship, you can get Sabin's best Blitz. At the middle north of the world map, there are some trees in the shape of a cross. Put Sabin in your party. Land, and walk onto the center tree. Go up to the house, and Sabin will learn his best Blitz, Bum Rush/Phantom Rush.
You can now fly to the continent northwest of the Veldt. The monsters that you can fight there include the strongest non-boss monster in the game: the level 77 Brachosaur/Bracsaur/Brachiosaur. The Brachosaurs/Bracsaurs/Brachiosaurs have a chance of dropping the Economizer/Celestriad, which makes all spells cost 1 MP. They are very difficult to beat, however.