I'm running a game now with a couple of different themes and factions. It's complicated, but this campaign is intended to go all the way to 20 (and maybe beyond). I'm still a pretty new GM, though, I've only been playing for a just over a year now. I seek advice on a few different things from you fine folks.
First and most important, how do I manage a game that takes place in two planes? I want the party to be spending their time on the material plane (my homebrew world) and the shadow plane (Jon Brazer Enterprises' Shadowsfall + homebrew stuff), with about a 65%/35% split for now. The thing is, they're level three. How do I get them to travel back and forth? They do have something of a mentor party of very experienced adventurers that can help them across, but I don't want them to be totally reliant. Also, how do I make the shadow plane really feel different?
I feel pretty comfortable with the aberrations and the prophecies. I've got cool ideas for those. The thing is, there are a number of major factions that I all want to matter and feel distinct. There's the drow, the dwarves, the elves (represented mostly by the lantern bearers, which one party member aspires to become), a kyton demagogue I have yet to detail, several human lords and a king, and the elans. That's a lot. How do you manage this many different groups with all sorts of different goals in a game? There might also be a resurgence of the ancient cyclops empire.
Just a note, the game is mostly open-world, with the players making a lot of decisions on story direction themselves, which only further complicates things.
I don't know how you'll do it, but I have an evil fairy tale game that's moving into a similar phase, also at level 3. You see there's the normal, material world and then there's the Twilit Realms.
These are supposed to be places of the primeval First World that have become tainted by the Shadow, a nebulous force of evil, sort of like the Powers of the Land from Ravenloft.
1. How do I move the party back and forth - through random fey rings. Being fey and mercurial the rings can take any form I want: a circle of mushrooms or flowers, the circular floor of a tower, or maybe an actual ring one of the PCs puts on. In essence I just put them in the other world when I want.
2. How to make it feel different - well, in the Twilit Realms there's a twinge of horror so I'm going to add elements I've gotten from other threads on building suspense and horror. For ex: the party in their next adventure is going to try and save a little sister/Red Riding Hood stand-in from an evil "granny" and this will take them through a weird field of wildflowers and a dark wood. As they travel there will be perception checks for noticing beady red eyes watching them, the smell of sickly-sweet honey, or a river of tar streaked with gruesome, rust-colored blurbs.
For me its about not just invoking the weird of the fey but then taking that and twinging it with darkness. I feel less is more and especially if we're talking horror and suspense you want to be vague on purpose so the players are foced to imagine the worst.
In regards to different factions...OMG yes. I have the same thing there too. My game has one PC with hags in her background though she's not a changeling, so I added a hag 2 generations back. She also wanted her character to owe some kind of debt inherited from her parents, but she stipulated it be monetary, so I created the Hexbane; a bunch of witch-hunter inquisitors who are blackmailing her family because of their bloodline.
Now another player had his parents killed by fey. Before I even wrote the main campaign I decided I wanted a villain related to his PC, so I added a fey faction out to get him and then a sister stolen to the First World and then escaped to become the Goblin Queen.
So in summation I've got an evil hag and her witches, I've got a cruel inquisition, there's the fey, there's the goblin queen and her goblin & worg minions, and then once I got going I inadvertantly created a 5th faction under the control of a wererat in an ad-libbed adventure.
I try and think of them as separate folks with their own goals and such. Rather than have multiple factions per adventure I compartmentalize; this little red riding hood adventure will have witches, then after that the worgs will be the target, then the fey at a wicked carnival and so on.
Now, could there be agents of one in another adventure? Sure. In Red Riding Hood the party will meet a worg; he'll turn out to be an agent of the fey in the end. But I try to make 1 faction per adventure so that it's not some major conclave just to resolve a single goal.
Portals to the other world.
Devices with limited uses allowing travel between worlds.
Simple incantation opening gateways.
Stepping into a mirror.
Natural ability of the players and other denizens that exist between worlds.
Curse.
Blessing.
*shrugs* It all depends on what you want out of it.
Greg