The map of the mountains is below.
1) The entrance after leaving Crossroads Castle
2) A chest with Jade Armour
3) A chest with some Potion Omega
4) Entrance into the caves
5) Exit from the caves
6) Some Elixir
7) Final Boss
The caves looks like this with the darkness removed:
1) Entrance into the caves from mountains1
2) Another Jade Armour
3) A Flame Sword
4) Save Zone
I recommend you wait to equip the Flame Sword until you reach the mountain Save Zone because the Wraith is strong against fire attacks (it will give him HP.)
When entering the Save Zone (4) a scene will take place and you'll learn vFire - but you can't just use it any time, because it drains 100% HP/MP of both players.
You can touch the pools in the Save Zone to heal.
The last order of business is to head to 7 in the top map and fight the final boss. After finishing and watching the credits, you'll have unlocked at least 8 of the 10 achievements.
The other two are:
1) Lucky Shot - you may need to fight some low level battles to get this - the Jade Sword is a good weapon to use because it has extra Luck.
2) One Sitting - to get this achievement, you'll have to play from beginning to end without ever loading or dying (one character dying is OK as is dying but being brought back to life by a Second Chance.)
Congratulations on finishing the game!