Yes the difficulty does ramp up on the second island. My strategy is to explore around the island looking for enemies I can beat and hiding/running away from the ones who are too difficult. Also I use the boat to hop around the island to explore, grab treasure and search out weaker enemies. I avoid the impossible ones but do try the others as sometimes you get lucky with your tactics and win. I don't think it makes much difference what class you've chosen, the second island is hard but it is doable with patience. Good luck :)

Sorry for the late post, but...

I have recently been playing Amelia as a Mage, so the answer to this stuff is very fresh in my mind at the time when I'm writing this post. If this post doesn't help the OP because he has already beat the game, then maybe it will help someone else in the future who has the same question.

First I played on Impossible difficulty, but after the first three islands or so, it became literally impossible for me to progress any further, unless I was going to take out a few units at a time of a specific enemy stack, and then get defeated, and then go back to the same stack again with the crappy free units that you get automatically once you are defeated...and then do this same cycle multiple times to take down that one specific stack, and then do this same cycle thousands of more times, for every single remaining stack in the game.

But that would have been way too boring and tedious and aggravating, so then said to myself, "no way am I doing this crap any more!"

And so I started over again on Normal difficulty.

It was still quite challenging even on Normal, but this time I didn't stuck, and I didn't run out of gold either (but on Impossible, I was always getting stuck and always running out of gold).

So my first advice would be, if you are playing on anything higher than "Normal" difficulty, then restart a new game on Normal difficulty...because in Crossworlds, Normal difficulty might as well be equivalent to "Nightmare" difficulty in most other games. Higher than Normal is not worth it IMO, unless we are talking about an e-Sports type of player.

My second advice would be to get the spell to summon a chaos dragon as soon as you possibly can.

Once you have that spell, then your life as a mage gets much easier, because you will want to be having that chaos dragon up on the battlefield for 100% of the time, for every battle, for the whole rest of the game. That will be your main unit for distracting enemies and drawing their attacks to itself.

And also it will be your main unit for taking out enemies (it has a lot of HP and also great damage too) (or maybe your second main unit for taking out enemies, if you have a stack of Red Dragons too...but you will want your chaos dragon on the battlefield, 100% of the time, either way).

Likewise, you want to get the summon phoenix spell as soon as you possibly can. Once you do, then in every single battle for the rest of the game, you are going to want to summon the phoenix on the very next turn after you've summoned the chaos dragon.

The phoenix will also serve all of the same functions as the chaos dragon.

You want to have both the chaos dragon and the phoenix on the battlefield at all times.

And you want to upgrade both of them to level 3 as soon as you possibly can (this will require magic crystals, which you can find on the adventure map, and from quests, and from salvaging gear...and you get more mana crystals from salvaging gear if you invest attributes into the "Neatness" skill).

And it will also require you investing attribute points into "Chaos Magic" and into "Order Magic" too; get them both to level 3 as soon as you possibly can, but Chaos Magic first, because the chaos dragon summon is stronger and more useful the the phoenix summon is (but the phoenix is still essential too).

Also, get your "Summoner" skill to level 3 as soon as you possibly can, because it makes your summoned creatures stronger.

Other than that, try to get as many Red Dragons as your leadership will allow you to have at given time, and use them for 100% every battle.

These are the best dragons because you can heal them, and you can resurrect them, and their attacks are very strong, and they hit two units at once.

You can find some Red Dragons on the Island of Verona (which is the first place you will find them, probably) and on the Island of Elon (which is the second place you will find them, probably) and the Island of Sheterra (which is the third place you will find them, probably).

The Black Dragons are strong too, but they can't be healed or resurrected, so that makes them worse than the Red Dragons...but if you need a strong unit, then Black Dragons are good too (you can find them available to buy in the cave on the Northwest side of the Island of Elon).

Emerald Dragons are really trashy compared to Red Dragons; you might want to use some Emerald Dragons if you haven't found Red Dragons yet, but for the most part, don't bother with Emerald Dragons, because their attacks are weak, and they only hit one unit, and their mana draining ability is completely useless. In summary, Emerald Dragons suck very badly.

Other than that, try not to fight stacks that are listed as more than "Strong." If the stack is listed as "Lethal" or "Invincible," then it's generally not worth fighting, because even if you win, you will probably take too many losses to make the fight have been worthwhile at that point in time.

So, this involves you traveling to different parts of each island, and also traveling to all of the different islands, and cherrypicking each stack you fight, one by one, and only fighting stacks that you are currently able to fight against reasonably (which like I said, that would be stacks that don't say anything worse than "Strong,"...but "Slightly Stronger" is okay to fight too).

When you are around level 40 or so, then you might be strong enough to stop worrying about stacks that say "Lethal" or "Invincible," so the advice in the previous paragraph isn't necessarily applicable to the mid-game & end-game. But before your character becomes very strong and experienced, then it is applicable.

Another good tip is to make sure your dragon has the "Treasure Hunter" skill, and upgrade it to the point where you can collect 3 treasures per battle, and then always use it, and always collect those three treasures in every battle.

This will increase your experience gain for each time when you get the 3 levels of the treasure medal, and it will also dig up many useful things for you too, including vital scrolls like the chaos dragon scroll, the phoenix dragon scroll, the resurrection scroll, and all types of runes, and mana crystals, etc.

Note: the dragon will also dig up useless trash a lot of the time too. But that's okay, because if you use him to dig up treasure every time you can, then sooner or later, he's going to give you really good stuff for sure.

Speaking of medals, you want to look at the criteria on your Inventory screen for each of the medals, and earn those medals ASAP. The Treasure Hunter medal is vital for the experience gain bonuses.

And the winning battles with no losses is vital for the Leadership increase bonuses. To win with no losses, you need either units that are much stronger than the enemy units who they are fighting are, and/or you need units and/or spells that can heal & resurrect your fallen units (i.e. Inquisitor, Guard Droid, Rune Mage, Paladin, and the healing spell, and the resurrection spell, etc.)

That's probably also one of the reasons why OP was having difficulty. Probably he took losses on the first Island (Debir), but that Island is actually relatively easy to take no losses on during all of the battles there, if you use the right units with lots of HP (i.e. Mage Hunter), and doing that should get you to the first level of the Leadership increase medal before you go to the second Island.

But players who didn't realize that taking no losses is in their best interest probably wouldn't have bothered making sure to take no losses.

Another trick I learned is to play the tutorial mission that you get offered shortly after you come to the first Island, and as soon as you get the Paladin units as part of the tutorial, then you should immediately dismiss all of your other units that are in your army at the time...because doing this will let you get one or two easy battles won with no losses, which counts towards your "no losses" medal (but unfortunately, the game takes the Paladins away from you after the tutorial).

One more thing, after getting Treasure Hunter on your dragon, the next most important skill after that, by far, is "Mana Accelerator," which you are going to be using all of the time in order to give yourself mana for your spells.