How should I make the fox battle in the forest, it's impossible... I've both Rose and Vuu at Level 9, is that the problem?
It's possible to beat her at level 9!
She does take less damage from purple spells though, so you might want to change your loadout. As for general battle tips, swapping characters in combat will restore some health, and high combos have a bunch of positive effects, even more so if you have combo spells equipped ^^
If it's still too hard, you can also lower the difficulty in the settings!
Glad I was not the only one who struggled with that battle. Yea, it is possible to get combo-spells by that point in the game. They help a bit and the tutorial about them isn't until a little past that point, so they are easy to miss.
But the biggest piece of advice I would have given myself for that fight is: if you lose your combo, just start the fight over. Avoid all the damage you can, but keep your combo going at all costs. It just makes everything better. Play around and learn the tricks that let you scam the meter to keep a combo going through resets and stuff.