Well... one could throw in all the various published worlds/settings as worlds:
Most of those are kitchen sinks, which I've already got covered. I'm probably going to use elements from each of them, but all that is taking place on the main planet-- before the characters get out to the stars.
Can't go too wrong with the Maztica setting. It should be fringe enough that most players only know it as "The Aztec setting". Fill your dense jungles full of odd midlife, giant insects, and it give you an excuse to use a Couatl.
Yeah. The more I think about it, the more I want to use Maztica influences for my jungle planet, along with a lot of reptiles. Figure populate it with Maztican Humans, cannibal halflings, and both barbarian and civilized ssurrans. Want to involve the Giff with this planet, but I'm not sure how.
Other theme's for planets:
- a world of floating islands with aerial races
Need to do this. I'm going to ditch the Mario world, but there are elements of it that'll still show up in the air world-- cloud castles, beanstalks. Got aarakocra as an aerial race, and they also show up on Athas... not sure what else. Probably a lot of immigrants from other worlds.
- a water world, no land whatsoever
Every Sphere should have a water world. I don't like aquatic people, but having all sorts of terrible sea monsters to threaten ships that try to replenish their water supplies here...
- blasted 'rock' world where all civilization is placed in the Underdark because the surface is too hot / too many storms / whatever
...
- a dark world where it always rains / there are always clouds: supports very little vegetation and animals, mainly oozes, fungi etc.
I was thinking a world covered in thick, dark clouds where the various Underdark races live on the surface. Probably never discovered spelljamming on their own because they've never seen the stars, but as soon as spelljammers discovered
them, all of the horrible races there plot to escape and wreak havoc on the multiverse. Frame the entire world around the conflict of the Drow and their Evil Outsider allies and the Illithids with their Aberrations. The Gith would obviously have an interest in the world, and I like the idea of having Gnomes caught in the middle.
There are few Sci-fi settings that would make great fantasy settings, esp. for an RPG campaign. This is one:
The Integral Trees
This is nice. I would have never imagined something like this on my own.