The Schism: A 13th Age RP Campaign

Totems are definitely a must. I also like Crow's Levi idea a lot. A couple other things we could try...

-Attempt to funnel the Thunder Legion into the bottleneck of dry land by making rushing through the stream dangerous, and/or thwart their charge with the potion of slippery oil.
-Bottleneck ourselves in the passage between the crags and buy time for someone to emergency attune to the castle helm (unless it would take too long, which I suspect.)
-Find some way to collapse the hill so we can screw over the shadow legion guys and bottleneck the thunder legion into the stream. Maybe we could accomplish this with the potion of Herculean strength?
-Climb the mountain and fight the shadow legion to force the high ground against the thunder legion, especially risky because their thundering steps gimmick could get us killed up there.

Any of this would really just be to mitigate the damage they can cause to us. I agree that spamming ranged and AoE attacks is our best bet to deal a lot of damage. Maybe Aeva will want our scrolls?

I'm not going to be around on the 9th this week. Saturday, I think? Yeah.

Important stuff to note.

The Meaningful Death Clause is invoked for Raikou. He is the first of the story bosses in the questline and is treated as a major antagonist. The other enemies can't kill a PC, but Raikou can.

Selene may or may not be able to use the Castle Helm. I'll have to check when I get home, is at Tax appointment now. I'm fairly certain Sephira can.

You can't attune to a magic item in the middle of combat, but I'm willing to be flexible and say someone could have attuned or un-attuned to an item on the journey over.

Raven's best suited to summoning, not using a totem. Ivory Lagi will be a life saver here.

The real test of this battle is how well you weather the initial onslaught. The Orc Troops who moved at the start of battle will all get another free move action, so they're pretty much going to instantly surround the party. Taking out a sizable number of enemies in the first round will make this battle significantly easier.

To that effect, Selene has Circle of Death and could potentially wipe out all the Orc Troops in a single shot. But that's risky, as it will do minor chip damage to all allies as well, which when combined with the chip Thunder damage the Orcs do when moving, could put allies into range for Raikou to deliver a potentially fatal blow.

Raikou gets to make a special attack as a Free Action as soon as his turn rolls around, in addition to his normal attacks, so that's something to remember.

It'll be fine. Aeva's going to take the brunt of their first turn, and they aren't going to get a second.

I'm not so concerned about not having the wide-area summons for Amatsu. Total damage dealt hitting everyone in a small army is way greater than... I mean, the point isn't to wipe them all out so much as chunk a lot of them down for mop-up. Save the big single-target stuff for Ammy and Raikou, open by using 1 or 2 to wear the enemy down. The highest priority is breaking their first charge so we can turn around and regain control of positioning before reinforcements start arriving.

Do you guys want Selene or Sephira to use the Castle Helm?

Selene.

Before I forget! The thing she's missing! It's, uh... wait, what's the word? For when you know everything's terrible but you also know you can't really do anything to stop it from being terrible so you're just like 'meh OK go ahead and tie me up or whatever it is you're planning tonight and I'll deal with that crap tomorrow'

...Temperance...?  No, that's not right.  That's like the opposite.  Indulgence?  Closer.  Also pretty much the opposite.

That... is very important.

I'm talking about that feeling of 'screw the consequences they come later, I'm going to do what I want right now'