The gimmick for the battle is that the enemy has high defense, so just use the support napoleon and use his np to chip down its hp

Three of those quests have support servants that will deal the required damage to get past the defences, while the last one is simply surviving long enough where the defaults are healers. Use the support servants the game recommends, take in servants to help them if you can (Waver NP battery, servant damage type, etc) and smash.

Ok, now my problem is with the southern treasure, what should I do?

Thank everyone who was kind enough to answer my questions, I really appreciate the help.

Just use the event NPC support. That's the game help you. Also read the strategic hint for each fight.

Don't forget the 2* Command Code that removes burn/poison/Curse. Just stack them to all your face cards, it should help a lot.

I used my Mash for that. Her 1st skill in Ortinax form worked just fine.

Wait, people actually willingly use that? (O_O;)

Yeah Napoleon got this

My team consisted of Mashu (has everyone) Cas Gil (at level 108) and Merlin. I don't need to mention the rearguard - since they never got their turn. The three are a very passive team and it took 45 turns - but I didn't lose a single one. The skills of the three interargue so well together that you always have an optimal defense. Think of it as a chain of shields - plus Merlin who also heals.

Many simply underestimate Mashu - as she becomes a beast together with Merlin - basically you could also combine any other Servant to it - as long as this one makes DMG and buffs the team. I prefer to use Gilgamesh Caster (because I like him) but there are certainly better alternatives.