Once you’re back on Estard Isle, board the Sea Dragon and watch the following scenes, with you receiving the Water Amulet. You will gain full access to the Sea Dragon at this time, which acts like your normal ship, but it will sometimes help you out in battles. Despite recent events, enemies can still be found on the world map, so you will still have to either fight or avoid them. However, you will regain access to all of your transportation devices, including Zoom, the Flying Carpet, and even the Skystone. You will also regain access to the entire world and all of its services, so you could make nee Traveller’s Tablets and go gamble some.
Speaking of which, with the final dungeon accessible, the casino at The Haven (assuming you’ve been following this guide and have every resident up to this point) has been upgraded with some of the better items in the game, so make sure you check it out. You can also open those locked chests in the one house, netting you some Orichalcum Fangs , Royal Mail , Malevolantern Heart and a Mysterious Fragment . You can also get another resident for The Haven, who is in Buccanham. Go to the top of the lighthouse and speak with the kingly person, sending him to The Haven.
Another thing you can do is go and turn in some Mini Medals at King Maximo’s Mansion, but if you happen to get a few extra from the StreetPass resident tower at The Haven (at least three more), then you can receive the reward for 105 medals, which is the Gringham Whip. This whip is the strongest one in the game, so it’s a good upgrade to any others you might have equipped. You also receive a Metal King Shield at 90 medals, which is a great piece of equipment.
Maribel will leave the party and Mervyn will rejoin. It is possible to get Maribel back into your party, by simply visiting her at her house, but there’s something that should be talked about prior to doing this. There is a MAJOR glitch in the game that can basically break it and lock your progression in the final dungeon, and it involves having Maribel in your party. Basically, if you trigger any scenes in areas where she was not supposed to be present, like the Great Leveller or in past scenarios when she was gone, the game will kick her out of the party while having her in the party at the same time.
It will become a ghost slot and you will not be able to have an actual fourth party member. So, if you’re not done exploring, do so without Maribel in your party and make sure you definitely keep a second save file in case you wish to use her again. This seems to be prevalent when visiting past Aeolus Vale, Vogograd and Buccanham, but to be on the safe side, just avoid bringing her along when going to visit the past places. There are a few other things you could do right now, like grind some levels or Vocations, as well as some other sidequests, but they aren’t important, so it’s time to head to the final dungeon.