Golden Sun: The Lost Age/Contigo Revisited

Back in Contigo, ignore everything for the mean time and head to the house at the north. Inside, Issac, Garet, Ivan and Mia will be waiting for you. After the discussion about why Felix is doing what he's doing, Hamma will show up and inform you that you've unbalanced the elements.

You now have your old GS party back, and if you updated your save, they'll own everything they did before. Djinni are the most important, because without all 28 from the first game you can't go into Anemos Inner Sanctum to get either Charon or Iris. You might want to take this chance to equip everyone with whatever they need and switch equipment around.

Unfortunately the only services available are the Sanctum, Inn and the minigames, since everyone's at Atteka Inlet putting the finishing touches on your boat. You can, however, get a Mars Djinni you were previously unable to. Go to the stump at the top-left of the main town area, and use Force (providing you got the Orb of Force transferred from the original game) on the stump to evict Shine, who will join your party without a fight.

Once you're done with sorting out your new additions, go back to Atteka Inlet.

Atteka Inlet Revisited
First of all, head down to the boulder in the enclosure at the bottom. Use Lift (providing you have the Lifting Gem) to lift the boulder up, then use Cyclone on the weeds inside to unearth Geode, the Venus Djinni! It'll join you without a fight.

Once you've got it, head back to your boat. Climb up and Hamma will be there to greet you. When you try to get on, a man will rush and drop off a chest. It is imperative you get this - it contains some Orihalcon, the best and rarest forgeable material in the game.

When you're ready, go ahead and set sail. The reef to the southwest, when on the world map, can now be hovered over using the B button. You can fly faster than normal when hovering, and reefs won't hinder you anymore (the rocky spires will, but the flat reefs won't). Another bonus of flying is that you won't get any random encounters. The downside is the meter above your boat - this is everyone Psynergy level. If you notice your party status at any point, and you've been using the flying mode a lot, you will realise everyone's PP will have dropped dramatically. So basically, use this in moderation.

Coatlicue
You can now get a combo summon, Coatlicue. Go around Atteka to the split beach on the eastern coast. Fly your boat along the coast southwards until you get to a short river coming down from a mountain. Fly over this, then go left inbetween the trees around to another short river coming from a mountain. Drop your boat either in the river or on the southeastern side, then get off and enter Atteka Cavern. Inside, go around to the right so you can reach the water with Parch. Use it to drain the pool, then go back around, climbing up and down ladders to reach the tablet. You can now summon Coatlicue! She requires 3 Jupiter and 3 Mercury. She does no damage however - her effect is a weak initial heal, followed by 3-4 turns of awesome health regeneration - basically, your characters regenerate just over half their maximum health every turn for 3 or 4 turns.

Get back on your boat and fly back to the sea. Now, you will want to head back to Yallam.

Back to Yallam, Again
You've acquired some forgeable materials you will want to forge - a Dragon Skin, some Dark Matter, and some Orihalcon. You can get what you want from the Dark Matter and Dragon Skin, but you can reload over and over with forging the Orihalcon to get Excalibur. Excalibur is one of the strongest swords in the game, not that far behind the Sol Blade. Its unleash is amazing, capable of doing at least 300 damage, sometimes even 800. So, fly down between Osenia and Tundaria. You can now use your flying ship to save time and fly over land around the rocky spires separating the two seas, and get back into the Eastern Sea. Head north to Yallam and forge your stuff.

However, you will be able to get some more Orihalcon soon, so it doesn't matter if you don't get Excalibur. There are a lot of other great items to get from it, like the Xylion Armour. Whilst you're here, you can also get another great weapon. Use Force (if you have it) on the log outside the blacksmiths to form a platform you can hop to. Over on the other side, use Cyclone to uncover a ladder. Go down through the cave and grab the Masamune from the chest. This is excellent on Piers.