Which Spell To Fully Merit?

So on the list of things to do is build a San/Ni spinning nin setup. Looks like fun!

Anyways, our merits limit us to maxing out 1 san spell (with 1 point in the rest) :(

So which spell to max? Does it matter?

I'm thinking Hyoton due to the elemental bonus on the 51 staff, but when I get 2xMAB/INT sekkas done that advantage will disapear.

I did Hyoton, because of the crazy ice atmas.

You mean because of the 5 INT on the staff? Really not a good reason to merit ice over anything else tbh. Atma of the Beyond, on the other hand, is a very nice reason to do so.

better make full Hyoton or half hyo and raiton?

I'm not a Ninja, but I'm guessing your choice of element probably doesn't matter a whole lot.

I'm hoping you know this already, but Elemental Magic Skill (like what's found on Ice/Aquilo's Staff) does not affect Magic Accuracy or damage of Ninjutsu spells. The hidden effect on elemental staves (MAB and Magic Accuracy) would apply to Ninjutsu spells, but that's available on all the level 51 elemental staves, not just Ice/Aquilo's.

One advantage of using Hyoton is that many enemy classes are weak to ice magic (yagudos, tonberries, crabs, pugils, mandragora, gnoles, monkeys, turtles, bugards, lizards, peiste, wivres, bees, beetles, damselflies, scorpions, ladybugs, spiders, traps, cactus, kraken, slugs, birds, ***, rocs, colibri, puks, gears).

The downside of Hyoton is that many enemy classes heavily resist ice magic, including almost all types of undead, plus gigas and several others.

I'd say Katon is a good choice. Not many enemy classes are resistant to fire damage.

Ultimately, your choice!

Staves are not MAB, they're a completely separate term.

hmm, where can i find a page outlining mobs strengths/weakness's?

Monster Classification Guide

This is a decent place to start, although I don't know that it's 100% accurate, and it needs updating for newer monster classes.