My Campaign idea!!!
I'm getting ready to run a 16th level start in the Dragonstar Universe. As the players are hanging up their swords for good, something happens that will bring the players out of retirement that could effect the universe.
The main bad guys: Mezzenbone(Dragonlord, Dragonstar and current ruler of the Empire), Iuz the Old(Greyhawk), Manshoon(Forgotten Realms) and one from Dragonlance possibly and one from Dawnforge
The main good guys: Eliminster(Forgotten Realms), Lovithan(my character from Greyhawk), Lazarius(Dragonstar and resurrected into a Dracolich or sanctified have not decided yet), and a couple others from the other settings mentioned above.
Using Dragonstar allows me not to be nitpicky and have portals open up to other worlds and would allow me. Just place the worlds where there would be confrontations going on. What I did was place the known worlds out there on the border of the Red Dragon domain and the Blue Dragon domain and bring back a dead high lord to fight the Red Dragon forces for all of those who have the Dragonstar universe and know what I mean.