AereA
28 Achievements
1,000
20-25h
Fortissimo
Upgrade all skills from all classes to level 3
50
0.81%
How to unlock the Fortissimo achievement in AereA - Definitive Guide
For grinding, Snow Mountain has the most pots (destroy them for clefines). I used area 1.
It's a long and boring grind, but faster than playing other levels.
Don't bother playing through the whole level, because you'll have to walk back and forth to open closed doors (passing empty areas); it takes to much time. When you've cleared a couple of areas, just quit to main menu and reload the game.
To unlock all skills, your character need to reach level 30. When you do you unlock the Legato achievement. If you need some level boosting, Lava Caves area 1 is the place to go. You'll level up a bit while gathering clefines, so there's really no need to boost your characters all the way to level 30 before going for this.
After unlocking "Legato", you will then need to max out the skills you just got to Level 3 with your Clefines. These skills can go past Level 3, but make sure you don't do that, as it is a huge waste of money (and therefore time).
The best place to grind money is the first snow mountain level, as it has the most pots, and the least amount of backtracking and areas without pots (unlike the second snow level which is much larger and confusing). Simply do a run, and then you can either take the teleporter back to the concert hall if you're near it, or just quit to the main menu. The game saves automatically, and when you load it back up, you will always spawn in the concert hall.
I would suggest grinding this in small increments. Each character takes about 25k to fully upgrade (the mage a bit more, the warrior a bit less), but instead of simply grinding out all 25k at once, set smaller goals and buy each upgrade as you can. It will make the grind feel a bit less daunting, despite taking the same amount of time either way.