Welcome to "Flooded Paradise", a mod that replaces the overworld with an endless ocean filled with reefs. I highly recommend using this with any mod that give you endless water breathing on joining, because the sea level is very high here.
Modpacks can use this, but do not redistribute this anywhere.
As of 1.9.0, I removed auto-spawning in the flooded paradise, as it would spawn you in water instead of on an island.
If you want to access the dimension, use any mod that allows customizing your spawn dimension.
