Help me flesh out an idea for a sandbox campaign

[Macona]

I really enjoyed running Kingmaker, so I’m working on a similar styled sandbox campaign. I want more of focus on fantastical adventures in a hostile & exotic location (similar theme to the works of Jules Verne).

Here’s what I’ve got so far:

A large tropical Island full of ancient ruins, dungeons and big monsters is discovered in the Azlantian Ocean. Various factions sail there to claim it as their own. The PCs start as freelance adventures who will be paid to explore and clear the island of monsters. The direction of the game will largely depend on the PC actions, but my hope is that they will eventually rise up the ranks of a faction and maybe use the kingdom building rules.

~Random thoughts and Ideas~
-The island has an ancient evil that gains in power. I haven’t decided what this is yet, or how it will specifically affect the PCs.
-The island was hidden, now it’s not.
-Lots of ruins of old races including Azlantians, Serpentfolk and Aboleth
-Dinosaurs!
-Other indigenous nasties

[Spastic Puma]

I ferociously recommend that you implement some sort of time limit for the party to complete their task. Maybe an impending volcanic eruption, an awakening evil being, or maybe the island goes back underwater after that time.

Time limits drive the game forward, and in my experience, work fantastic with a sandbox. The best campaign I ever DM'd was a heavily-modified version of another pathfinder module where the party has 60 days to clean up a small section of land for a king (I can't remember it's original name).

[EWHM]

I'd suggest not setting any particular time limit, but have the various other factions doing their thing according to a timetable. Set their various milestones (assuming no interference, such will obviously delay them). So, for instance, if you don't investigate the Tomb of Aroden by D+50, faction A will already have begun doing so. Faction D will begin investigating it on D+75, and so on.
That's how you get time limits that AREN'T artificial and metagamey.

[I Hate Nickelback]

The time limit doesn't have to be metagamey.

The party could meet a wizard researching the island's mysteries who says "the magical pulses emanating from the center of the island match perfectly with extraplanar resonances from eldritch ionic machinations. If my readings are correct, these pulses should induce a pseudo-eldritch implosion that could drive the island back underwater in X days" or something. Note that the words I said have no intrinsic meaning with each other. :P

[EWHM]

I hate nickelback,
What you've described smells metagamey to me, and would certainly smell such to my players. The only way I could walk it is if I'd placed the proverbial shotgun well in advance (prophecy or astrological prediction that this island will rise from the sea in Year X and vanish beneath the waves again after Y days). Otherwise my players would rightfully estimate that the time limit is there because of an external cause rather than an internal one. Now a race between factions, that they'll swallow as internally caused nearly every time.

[williamoak]

Hey, how about your "ancient evil" ties in with player actions: The more things they kill on the island, the closer it comes to escape. Sort of a "whole island is a sacrificial altar". A time limit wouldn't be necessary, since it would be player action that would decide the outcome. However, clear time limits can give a good sense of urgency. However, it would avoid a volcano threat, since there still being accessible ruins wouldn't make much sense. I like EWHM's faction idea though it could fit well with another idea of mine:

Do they decide to keep slaughtering the natives, and risk releasing the evil? Or do they fight the other explorers to prevent the evil from escaping? How do they balance killing? You could have a giant hourglass in the center of the island where a grain of sand would fall each time something with a soul was murdered on the island.

Heck, that could even explain the ruins: There was a previous (failed) attempt to release the ancient evil that killed everyone!

[williamoak]

In any case Macona, you've given me some good ideas. I think I'm going to try to work on what I proposed in my last post. Could lead to some interesting shenanigans.

[Spastic Puma]

Wasn't that the plot to the first Warhammer 40K: Dawn of War game? That was a really cool twist when I played it.

[Tin Foil Yamakah]

What you are describing sounds like a mix of "The Isle of dread" and "Lost".

A friend of mine is running a campaign along those lines, with the island being home to a group of necromancers that is trying to establish a power base away from prying eyes.