Ok, some thoughts after reading through the whole thing.
1 Someone has already mentioned the possibility of the dark titan showing up in the final battle. Can he be tricked into fighting the good guys, or will he always prioritize whoever has the ring?
2 If I were running the campaign as a player, I'd surely start a side project of trying to turn the Nameless King's machine into a weapon of mass destruction (linking it remotely to the royal scepter, so it could dump the accumulated negative energy onto the battlefield.) Do you think it would work?
3 In the "two solars" version of the final battle, the PC's allies flee, except for Grumblejack. What about Sakkarot? If the players take him (obviously disguised) to fight by their side, would he flee too? He seemed like a very fatalistic type.
4 It bothers me a bit how the whole might score thing ends up largely cosmetic in the end - no matter which side is outnumbered ten to one, it will be down to the fight between the leaders in the end.
5 There are two courses of action that seem very logical to the players, but aren't described in the book at all.
5a - countering the princess' efforts in the mainland. Yes, she's permanently veiled, but a gathering army of thousands is much harder to hide, and if Dessiter gets some intelligence info like he was supposed to, the players might come up with a plan to delay her - hitting (or bribing) her potential allies, or perhaps persuading the kraken to harass her fleet en route.
5b - search for Anthea's lair. Even if the players haven't figured out she's their enemy, her treasure is the last major unclaimed hoard in Tallingarde, and the players are conquering the north either way. With some initial clues from Polidorus' book on dragons, they shouldn't have much trouble pinpointing the lair - and I'm pretty sure it wouldn't just be a frozen cave with a pile of treasure and a bunch of guardians. I really wish there were some more descriptions for it.
So, has anyone tried writing up Anthea's lair?
I'll give you some feedback:
1) The Thanatonic Titan from the Ring is basically an evil genie, in the sense that, when freed, i can be a powerful ally like a terrifying enemy. He's extremely intelligent and possibly somewhat aware of the situation of Talingarde throught the ring-wearer senses, if you so decide. However, by design, he's an enemy boss. If freed he should try to claim dominance over the land of Talingarde. If this requires to ally with the Pcs for a few fights, he will do so, but be sure he'll greater vital strike any creature that might oppose his rule the second the princess's forces are defeated.
2) The machine is not a cannon, unless you actually build a cannon over the Aghatium. Which is complicated. However, by design, the machine could be use to "create" and "bottle up" negative energy elementals, which could be deployed as weapons in a battle. Other, more sofisticate uses, are up to you.
3) The "two solars" scenario is build to stagger your players giving them a CR 25 fight, but since no creature exist with a CR label clearly visible, very few of the Pc's allies could infer their power, and therefore fall into despair. Who escapes this battle, if any, it's up to you.
4) By my understanding, the adventure it's heavily focused on getting control over Talingarde, which gives pcs little time to look outside the island for the princess. Nevertheless, you could arrange a number of situation, like discovering a few named npcs that your pcs may discover have been visited by the princess, and that may actually be interacted with.
As as example, i would suggest: 1) a monarchy allied with house darius 2) some other dragon (i remember the name of an ancient gold dragon offered by mr Mcbride), and possibly some kind of Azata/fairy princess.
5) Antharia's lair is a good place to visit, but should be almost empty. Antharia is, by the book, currently plane hopping with her daughter searching for allies. However, if you want to give your Pcs something EVIL to do, they could discover inside the almost void lair some kind of massive forge were Antharia's colossal mithral armor is being forged. They could either destroy the forge and steal the mithral or, if they are smart, try to intercept the dragon when she comes to put it, or even put high level curses on the piece, so that when the dragon wears it something very very bad happens - possibly during the battle, so that Antharia does not have time to counter it.
So, has anyone tried writing up Anthea's lair?
Not that any of my groups ever got even remotely close to this section, but I always had it ready to literally steal the silver dragon lair design from the 3.5 Draconomicon (page 266) and went with CR 18 dragon horde wealth (page 283), not including the mithral armor being created.
BTW, did anyone figure out just how the Princess ended up with Cha 40? Even with a tome of leadership and influence +5 I can only figure she's got a 38. I'm using the point buy calculator to help with this.
Her base stats are 8, 10, 14, 10, 14, 18
Human +2 to Cha
Sorcerer 20 bonus stats +5 to Cha
Half-dragon template +8 Str, +6 Con, +2 Int, +2 Cha
Headband of Mental Superiority +6
This gets her to 16, 10, 20, 18, 20, 33
Not noted, but let's assume she actually did read a tome of leadership and influence +5 to get her to 38 and Gary just forgot to make note of it. Where's the extra +2 come from to make it 40?
I'm dumb. After all these years, I finally broke it down and figured out what Gary did, and why the princess is "elite". It would have been so much easier had he just kept the original wording. The missing +2 comes from her being a dual-talented human. She gave up her bonus feat and Skilled human abilities for an additional +2 modifier to a stat. However, Gary did it wrong. You have to pick two separate stats, not the same one. This may have been an interpretation error or this could be something changed through errata and I'm just not aware. This also explains why she's missing a feat. As well, a few of the skills seem off because it looks like Gary may have mistakenly added in the trained +3 bonus to one or two of the skills. Namely Fly. Even if you have 1 rank in it, if the headband gives you max ranks, it only gives you the bonus as if you had max ranks in an untrained skill.
Basically, her stats should be more along the lines of 16, 12, 20, 18, 20, 38. Actually, better still, make her the equivalent to Azlanti, and give her +2 to all stats. That doesn't even give her a +1 CR because Advanced is +4 to all stats and +2 natural armor. It's an evil loophole Paizo came up with, but it works. She'd be a true elite in that regard.
I'm glad to have finally figured out what I was missing in regards to her stats.
What's funny is that today, because she's a half-dragon and really only gets the benefits of blindsense 60 ft., you could easily take the variant capstone and give her +8 to various stats. This could be +4 Dex, +4 Cha or it could be the full +8 to Charisma, because she has Perfect Body Flawless Mind.
If blindsense is something you really want to keep, the 3.5 dragonsight spell would be fine as a scroll or even a 1/day item.
1 The Hecontires is really scary, I seem to remember my players felt it was more dangerous than anything else in the campaign and set up an impressive trap for it and burned multiple wishes to get it to go away. It is intelligent, ruthless and wants to destroy everything . So it could be manipulated but only with extreme difficulty and then after is has slaughtered the good guys , the forces of evil still have to kill it.
2 If you have a character who is a skilled techno arcanist , spends a lot of the book6 downtime and resources of the kingdom working on it why not. It slaughters a lot of the army (possibly both armies) and now you have hundreds of soul sucking wraithes messing up your country
3 This is all subjective, If I had used the 2 solar ending the pc;s would have just killed both of them. I had to boost the final battle a lot more with all sorts of extra's but I let my party pick up lots of powerful enhancements like vampirism and being grave knights as well as crafting their own gear.
4 Live with it. The nature of D+D is that the small party of 20th level characters can slaughter most armies unless blocked by peer level opponents. My players made this point to the princess and there was no battle , the pc's fought the princess and her elite guards and the army of the losing side surrendered or fled the country. The Gravekight antipladin could probably have killed an entire mortal army on his own without the others helping him
5a - Dessiter is small fry the Princess is aided my many eqully capable angels and in the same way Asmodeus prevented the witch hunters running down the pc's Mithra protects the princess. Sure let the players spend a lot of their time and effort on this instead of securing their kingdom , let them wipe out a bunch of minions as you said above it won't matter at all at the final showdown
5b - I assumed the Dragon had moved out with her horde and was using it to fund the army of light, so my players never looked for her lair