1. Why even bother with getting a high level?
Well first because it helps you against the Mega Dragon which is about the only hard fight in the game and because its nice to have a high level.
And what would you consider a high level?
I would say anything above 100. 100Is a level you should be able to reach without much problem anyway.
What is the problem with reaching a high level?
Its not the experience points. At least not if you want to go to a very high level which will require grinding.
So whats the Trick?
The trick is to use the level boosting stuff as late as possible. At first this may sound a bit annoying because of backtracking but there aren't that many and most of them are late game items anyway.
So where do I find these boosts?
First a word about the Cloudside boosts, they are all +1level and if you think you need the level earlier or don't want to backtrack to them it won't matter that much
a) at the clouds above Witch Tower, in the lower left corner there is a cloud isle that can be reached with the jump spell. If you use the statue everyone gets +1 Level
b) in the Golem Dungeon, At the end of the dungeon is a Statue that gives you +1 level. Backtracking there is a bit more bothersome so if you want to save it up explore the iron part only at the endgame. The dungeon has nothing else of value in it.
c) Shangri-la The city below the lava cave. The well gives you +1 level if you drink from it and can easily be reached with the magic mirror. You have to go here later anyway because there is someone that teaches you all skills and one of the level ups on Darkside removes all secondary skills.
a) The druid that wants her statues back outside of Castleview. When you bring her back the statues you get +5 levels.
b) in the eastern tower there is a well that you will eventually reach when you use the northern stairs. It gives +5 levels and removes all secondary skills. So you need to go back to Shangri-la to restore the skills. This will cost you 600000 Gold total.
c) The dungeon of Alamar's Castle. The Power Juice gives 5 levels and can be used multiple times. There are enough to level up all your characters once and there are additional Juices to level each character again. (total of 12 +5level uses)
d) above the Dragon Tower. In the clouds there are several Crystals giving +3-5 levels. The value is random so save and reload until you get +5 from the crystal.
e) in the basement of the southern Sphinx there are Potions granting levels.
f) dungeon of death. After solving the crossword puzzle you get +5 levels.
When should start using the level boosts?
a) you should have explored all dungeons available before uniting the worlds. At the point where you reach the clouds above the Dragon Tower is a good point to set a Loyds Beacon and teleport to Olympus afterwards and use your Gold for leveling. After that all the dungeons mainly have items besides the Southern Sphinx which has one 2mil gold treasure. Make sure to keep at least 600000 Gold to relearn your skills lost from the eastern tower well. Maybe some additional money for repairing and other regular spending.
b) After collecting the 2 million from the Sphinx. This will give a few more levels but you have to backtrack to the dragon clouds and the basement of Castle Alamar because you have to save the level boosts there.
c) After finishing every dungeon besides the dungeon of death. You may a) spend your money before finishing the crossword puzzle for leveling and then wait with the other level boosters and level again after finishing the rest of the dungeon because you gain a bit of money from the items in the dungeon when selling them.
Note that b) and especially c) don't give you much of an level advantage to justify the additional backtracking.
I want to level even more where can I get the gold for that?
a) buy items in the store without any prefix, enhance them, resell, repeat for an eternity to gain enough money
b) go through the gemstone mines, make sure to get enough gems from the vines. Whether you get gems or the specific gem items is random. The vines have levels and higher leveled ones will give more gems than lover leveled. After using the vine the level is decreased by one and when it reaches 0 the vine is depleted.
After you have gone through the mines go to the lord of minerals sitting in one of the mines and give him 150k gold to replenish the caves.
Now go to the smiths in the tents at the poison lake. You should only use the ruby and maybe emerald smiths if you don't want to lose gems. Let them make an armor. If you want to optimize the process save and reload until you get a plate mail because they are worth the most. Sell the armors and repeat the process until you have enough gold.
Is there a way to get more gold while playing the normal game?
Yes but it also needs some save scumming. You have to save before you gain a treasure. Most treasures are random chosen from the tier list of that treasure. The most valuable items are amulets or plate mails with the best material prefix available in that tier.
Now how do I kill that Mega Dragon
First the roles your characters play in the battle:
Barbarians/Knights: They will be attacking, maybe using potions of GODs! if you have some left. Make sure to give them backup weapons because all there equipment is destroyed when they are eradicated.
Paladins/Clerics: They will cast resurrection on eradicated characters, use divine intervention if someone is ko or low on health or use mass distortion in that order.
Sorcerers/Archers: Attack when they have an intact weapon and the dragons hp is high, cast Dancing Swords if their weapon is broken or the dragons health gets low. They also might use potions of GODs!
Druid/Ranger: Heal KOed Paladins or Clerics or Attack.They also might use potions of GODs!
Preperation: there is a well that gives +1000 Spellpoints in the mountain near the 2 tents in the north of the ice reagion of darkside. Use it you only loose them by using them up or by resting. Then there is a well that gives +2500HP in the northeast corner of the world in the fire region. The same rule aplies like with the Spellpoints well. Then there is a well in dragon head at the dragon clouds. It gives you +50 levels. These should be enough. Now go to the point on the road where you can to teleport to the mega dragon, cast Day of Sorcery and Day of Protection, select the teleport spell but don't cast it yet. Now save and you are ready to go.
For the fight just use the characters like described above. There is still a lot of luck involved and you can fight more offensive if you want to.