What's the class of the strongest boss in the upcoming story/events? Thinking of grailing a servant vs it.

personally i dont think i would grail any of your servant.
probabily nero (who i envy you)
if you are looking to grail someone for pure gameplay prospective, then here 2 tips.
do it for damage. normally extra hp are less worth then extra attack.
you can chack the growth after their limit in this site servant page.
some servant benefit more for extra level then other ( like most berserker , cu alter, raikou)
For exemple, if you grail rama to 90, his damage is going from 9854 to 10888
thets pretty good.
try to look for thet.
support like el malloi dont need extra stats (unless you want hans to have a little more hp

Martha Ruler is a solid option, she has 1.1X dmg multiplier, and works a lot as a reverse triple B berserker (neutral damage on almost everyone, takes less damage from almost everyone).

Nero is a quality survivalist, do grail her for more HP.

Maybe Rama, he can dish crit dmg a lot.

Don't grail Assassins and Casters, as they gain far less effective attack from grails (0.9X dmg multiplier).

Mary would get more HP, which is bad, you want to keep her HP as low as possible...

Roll until you get Astolfo, and then grail him: https://www.youtube.com/watch?v=98I85vr336I

Yes, that's an Astolfo soloing the Final Boss of Part 1. That should give you an idea of how strong are the bosses on the near future, definitely not something you want to use grails for.

Btw, good call on Raikou.

Lol i'm grailing my servant for fun and also grailing for my favorite.
Playing for fun while waiting for your Raikou Lancer/Zerker to come and i think grailing for memes is worth the shot.

For Dragon Slayer Memes : lvl 90 ++ and lvl 80 ++ Georgios.
Roda roda da ! : Martha Rider and Ruler lvl 90 ++.
Whassup Homies Swag Yolo : Marie Caster lvl 90 ++.
Yo i'm da best supp ever : El Melloi lvl 100.
Always reduce your HP : Anne and Marie Rider 90 ++.
Ultimate Suicide Bomber : Arash lvl 90 ++.
Toughest Cockroach Anchor : OG Chu, OG Nero, Heracles lvl 90++.

For gameplay, i would suggest grailing for Martha Ruler or Nero.

The two I have heard of are Rider (guess who) who can't be damaged by good aligned servants and half damage by evil ones. And there's a fight with 6 bersekers that charge their np each turn. At least that's what my in-the-know friend says. Someone please correct me if I'm wrong.

I personally am thinking about grailing my np 2 Carmilla, but haven't decided yet.