Dhaos disappears just before you can defeat him, but a letter from Morrison gives you hope of finding Dhaos.
During the cut scene, you will be automatically healed up. After the cut scene, you should go to Midgard. You will need to go east to Alvanista first. If you didn't race the kid in Alvanista to get the Cat's Eyes, do it now.
From Alvanista, go east and south to the dock to Freland, then go east and north in Freland to reach Midgard.
Use a Rune Bottle on the Jade Ring that you won from Dhaos to turn it into a Fairy Ring.
Buy supplies in Midgard if you need them. Rest in the inn and watch the scene if you didn't see it before.
IMPORTANT: Before leaving Midgard, talk to the young woman in the north part of the city who is standing by a tree.
Then leave Midgard and go to the Valhalla Plains.
To reach the White Forest, go north three times, east, north, east twice, north four times, west, north, west twice, and north. Walk into the forest.
The White Forest
You will control Mint and Arche. You will not be attacked while you walk around the forest. If you want to leave, walk up to Cless/Cress and Klarth/Claus.
Go right, then go right again, and collect the mushroom. Then go left, use the bottom left exit, keep going south until the path splits four ways, and go left and collect the mushroom. Then go back to the four way screen and go down, and collect the mushroom there. Once again, go back to the four way screen, and now go right, then down, and get the mushroom. Go north, then go slightly up, get the mushroom behind the rock, then go up until you reach another four way screen. Keep going to the right until you reach a dead end. There is a mushroom there behind a tree.
Go west one screen, then keep going north. Arche will leave. Keep going up.
When you are in control of Cless/Cress, set his skill to Tiger Teeth, and equip a Moon Falux on him. Have Klarth/Claus ready to summon Luna.
Go to the right, then go down the bottom-right exit, go right twice, go down, and talk to Arche there to get her to join you. Have her ready to cast Ray. Then go straight up until you reach Mint and the Unicorn.
Tiger Teeth works well in this battle. Use a Flare Bottle on Cless/Cress to do more damage.
After the tree is saved, equip Mint with the Unicorn Horn. Go to Beladum and rest there, then go to Venezzia.