Final Battle Suggestion. (Spoilers, obviously.)

[Crim, The Red Thunder]

Does that mean she also has an orb of many ways, considering that's what you use to enter the last fight?

You could introduce an item that opens up a portal or acts as a summoning thing. Then when you enter the last battle you get a popup and choose a friendly faction to use it on.

Zemekkys studied the orb and developed spells/prayers/methods for utilizing portals without the actual orb itself.

Zemekkys cloned it the way that Tannen did.

The orb sorta makes the portal active, rather then actually MAKING you go through it. After you made the portal start up, anyone could wander through, maybe for X amount of time before the portal would have to be started up again.

For Linaniil, Tannen made mutiple copies, and she found one.

There ya go, problem solved. Pick the solution you like best, though in terms of Lore, I'm betting that the third one fits best, with the first one being second best. (If Zemekkys could do it, surely Linaniil could do, so that solves every problem too.)

I agree with one helper of choice, though the idea of the world converging on this mountain to save the world is nifty, but one seems more... balanced Either is acceptable, so long as the almighty Linaniil is one of the options.

[Dwindlehop]

Different kinds of helpers are reasonable. However, Linaniil in particular is probably unreasonable. She does a lot of damage. If the fight is balanced around her damage output, tankier characters are going to have a hell of a time if they do not bring her.

[supermini]

I am not in favor of adding more npcs to the final fight. The more you add, the more you're relying on npcs not being idiots and less on your own resources.

You can already see the randomness (and someone pointed it out in a post recently) with Aeryn - if she grabs Elandar's attention and you can't get it away she is toast, and the fight just got a LOT harder for you.

Aeryn's really the perfect npc for the final fight because she's tanky, and you don't really expect her to do anything except stand there and take damage. Even the AI can usually do that without screwing it up.