Creating and "Optimized" Adventure.

[Midnight_v]

"We are the Reforged. You will stand down and prepare to be upgraded. Resistance is futile. Comply or be eliminated."

I'm not sure if your referencing something or if thats a suggestion. You get the idea. I'd like them to not all speak english so sometimes its just mechano jibberish but yeah thats along the lines of what they're doing.
Moreover, I just looked at the unapprochable east and they have a Blightspawed that is a disease that turns you into a plant. So there's our slight modification.

[X-Codes]

Disease isn't dangerous for PCs, but when applied to communities they can be quite devastating.  If you infect enough people with them, some of them *will* die.

Some house rules to give Diseases potential without too much work:
1) When a disease reduces any ability score to 0, not just Constitution, the victim dies.
2) While diseased, you don't recover ability damage.
3) When a Heal check is made to aid your recovery, the check has a DC equal to the save DC of the disease + 4.  Success means the victim gains a +4 bonus on their saving throw for that day.
4) The Contagion spell can target an area as opposed to a creature.  In this case, the disease has the normal incubation period.  The area must be appropriate for the disease being created.  For example, Blinding Sickness can be cast on a river, and anyone drinking the water from the river would have to make the appropriate saving throws.

Mummy Rot, Ghoul Fever, and Blinding Sickness with these rules are all good diseases to inflict upon NPC communities.  At the low levels you're starting the campaign at, they might even pose a threat to the party.

[Midnight_v]

I've been rolling around the last few days looking through dm'ing sections of various boards.
Looked hard at the disease thing, and came up with a few interesting concepts, I also realized theres a lot of... different ideas about dm'ing, but thats an aside.
Here's the deal though, any thing that has natural immunities works pretty well, constructs, plants, undead are all awesome. Traps are hella important to the adventure, as well as monsters that works with the traps. Dungeons and wildernesses are both needed to keep the adventure varied.
The game changes considerably as more methods of travel becaome available, we knew this, but most modules don't take that into consideration and have 10th level ship adventures but no reason why. (The only reason that seems valid is "No ones been there, you can't teleport there because of this and its dangerous to attempt to do so)
  I realized too that I hate a maguffin.
So the disease thing is brilliant, because it really brings the game, w/o shoehorning really.
I reread the elder evils book, I'm a fan of that I realize I remember suggesting it to a dm here who's "evil players ran amok" I was like "Wake up an elder evil, its hard to be a petty thug in the backdrop of oppresive cosmic power when you're one of the few people who can stop it.
The Mechanoid invasion works, espcially with a diseease  that turns people to bots, making it an anethemic sign is awesome, as it scale with the party and happens until they stop it.
The undead king is covered quite a bite, in the Elders evil book when they send Galactu*AHEM* Atrophus to your world, if the undead legion thing has been done to death. Plauge of undead is naturally virulent so its not something you NEED to mod really
.....
The other would be something I'd call "Against the fey" Tenatively. Mother nature called, she's sick of your shit.
The main antgonists of this would be the Plants and fey really, but druids would be there of course, and it' give some use out of the Kiloreen... and you can totally make it a horror scenario pretty easily.
I don't know who the big bad would be and I'd have to make that, Oberon wakes up from his ancient slumber or whatever.
The Elves are fired as protectors of nature, pissed off trees start attacking, a disease that turns people into triffids, seems to be spreading. . . these are the concepts. Next I'm going to start collecting monster for each idea.
If you have any ideas  for them a priori, or any issues with the choosing of those specific enemies, or adventures, reasons they're not optimized for example feel free to add or pick those idea's apart.

[X-Codes]

The Mother Nature thing looks good on paper, but then you realize just how few Plant- and Fey-type creatures there are in the books, especially ones with high CRs.  That said, Druids as BBEGs is a good idea.  Their versatility is pretty awesome, and since they only need Wisdom and Con you can pretty safely give them a truckload of HP and high defenses.

[veekie]

Hmm, where does it cross the line from optimal to frustrating though?
The misdirecton strategies(invisibility, using Images to make false targets etc) are pretty nice as a player, but from the monsters it becomes an insoluble problem easily.

[Unbeliever]

The Mother Nature thing looks good on paper, but then you realize just how few Plant- and Fey-type creatures there are in the books, especially ones with high CRs.  That said, Druids as BBEGs is a good idea.  Their versatility is pretty awesome, and since they only need Wisdom and Con you can pretty safely give them a truckload of HP and high defenses.

Would elementals work, too?  There seem to be more than a few of them.  There's also the plant templates that can be added to lots of creatures, but that can be more work.

[Midnight_v]

The Mother Nature thing looks good on paper, but then you realize just how few Plant- and Fey-type creatures there are in the books, especially ones with high CRs.  That said, Druids as BBEGs is a good idea.  Their versatility is pretty awesome, and since they only need Wisdom and Con you can pretty safely give them a truckload of HP and high defenses.

Honestly thats why I've posted this here as opposed to a dm forum somewhere I know you'll know.
I tried to get away from a top down design but looks like its needed, I'll look for plants and well shoot them down/advance them. I also wasn't going to start with the Gaea's pissed thing but since you mention it lets start there.
Top of chain is:
Big bad: This will require work because it's gonna be one of those Elder Evil tihngys Sign looks like Appauling Fecundity.
Bigbads Angels AKA The Dragon: Now I'd like these to be some inhuman plant critters, if there nothing natural we'll template something with the green bound template, or the Blightspawned template and let it roar.
Leaders: Likely Druids, and Warlocks of fey descent, I know thats likey 4th bleed but still.
Elites: Again Druids and warlocks of lower level, but also all variance of plant monsters, green bound and otherwise.
Brutes: We can easily find plant themed brutes.
Minons will be horde of various fey and they can be all over the place doing all kinds of things.
I think the elementals will be call into it, cause nature dudes tie to them easily so Unbeliever has a great idea there.

The primary enemy Race Will be Killoreen the second will be Briaxarus or whatver the spelling of that is statted to you're liking but we can also use combinations of thorns, nymphs, satyrs' and all the traditional nature critter as well as things like yellow musk creepers etc.
I'll go looking today for high level and or Templatable critters for our enjoyment...
So the campaign ends with the death of the bigbad and the ramifications of the elder evil sign reaching El 20.

@ Veekie again the purpose of this thread at least in part is to define that line as well. We don't want the players to run around not knowing what's going on, or CONSTANTLY be ambushed, but thats a part of the game sometimes thats going to happen, sometimes you show up to late.
However, at the end of this, its will be an Avengers adventure, not a JLA adventure, you will be allowed to inevitably punchout cthulhu with or without the maggufin.