1)Kinda like secret base
2)Connected by bridges (Still not certain)
3)Can visit each others islands
4)50x50 wide
5)Invite friends
6)Access to chisel at limited use (Still not certain)
7)Sky island host can set a mini-game on sky island to play with friends (Still not certain)
8)Can make your own gym.
Regular:
1)Just regular survival
Both of them include:
1)Missions
2)Shops
3)Pokemon centres
4)Awesome gyms