Stats: Mave = 8,000 HP, GotS = 4,200 HP
Skills: Heracles Blow -> strong single target physical attack
Destruct -> very strong magic attack to whole team
Resistance change -> changes physical/magical resistance
Rewards: 80000 EXP | 10800 Gold
Battle Reward: Ultimate Save

The main point you have to keep in mind is that Mave switches her magic/physical resistance every turn. That means you can’t deal any damage with physical or magic attacks against her if she has the respective resistance active.

If you know (for example) that she has physical resistance active, and it’s your turn to choose actions, then let your melee characters use physical attacks, because Mave will change her resistance right at the beginning of the characters actions - before any of your characters can make a move. So, selecting magic attacks when she has the physical resistance up will result in no damage, because Mave will activate magic resistance before your characters move again.

I think it’s good to have two physical and two magical characters in your team to be able to inflict decent damage each turn. The main hero, Grieg, Oreana and Milka works just fine for this task. If your physical characters attack let your healer (Milka) use All Cure and if your magic characters attack then use All Cure with your main hero. The other physical or magic character that is not attacking can use buffs, debuffs, additional healing or resurrection.

Shadow Flare is particularly effective against Mave so use this as your standard magic attack (both Milk and Oreana can use this attack). On the other hand, use Rapid Slice and Heracles Blow with your physical characters.

Sometimes the damage you receive is too severe for you to attack each turn, and maybe even two of your characters die, but if you use a Revival Potion to resurrect your team members they are likely to survive the next turn without healing. Just be patient and keep up a constant damage output.