guide me

in that case david is my go to servant in such battles
he pulled my ass through rashomon and onigashima.
he his second skill has a 6 round cooldown which almost all bosses take that long to charge their np,a small 800 heal and a charm, stun remover
his first skill is a %50 defense buff with a decent heal that lets him stay on the field and support your team for longer
his third skill is a decent ranking charisma attack buff that never hurts to have
his attack and health stats are one of the highest of three star servants and three arts cards to spam his skill locking buster np making him an Excellent choice for long and harsh battles(unless the boss is a lancer lmao)
I would max his first and last skill too if I could spare the materials but right now I'm dealing with arjuna
second is mash her skillset is pretty self explanatory
if you have finished camelot her first skill gets a 2000 damage reduction PER HIT for a rouns which is like davids second skill in terms of damage repelling but with a shorter cooldown and a defense buff without the heal and debuff removal. level this first
her second skill should be leveled last since it has the Lowest improvement in terms of leveling. it is usually coupled with her third skill to render single target np's useless
her third skill when activated has a taunt HOWEVER this skill also ridiculously increases your np gain for a turn which can fill your np with two arts cards most of the timem I recommend reconsidering when to combo these skill hence they might be wasted when stacked
in terms of berserker preserving.mash is better,defense buffs are much more valuable to berserkers than attack buffs
during bosses lumping together a bunch of offensive servants wont do you much good, like putting a bunch of candles in one place,you should focus on supporting a single servant and have two support it and make sure it stays on the field as long as possible (herc but if class advantage is available choose rider. berserkers do only %50 more damage while class advantage does %100 more)