I've noticed a few major issues with the player and entity handling when the player leaves the Skylands dimension by falling to the void using an entity as a vehicle(boat, minecart, etc.).

After the player gets teleported back to the Overworld, things starts to get weird. Firstly, the entity which the player was riding is suddenly missing. On top of that, no new terrain in the Overworld is loaded other than what had been previously loaded during the same session. It also seems like there are spawning an absurd amounts (about 200 per second) of new mobs (entities) in the Overworld, mainly large amount of squids in water have been observed. This amount of entities cripples the performance, and is almost guaranteed to force the game to a stop.

After restarting the game and enter the same world as before, you spawn at the same x- and z-coordinates in the Overworld as where you left the Skylands. However, you also spawn inside blocks at bedrock (y0-y5), together with your ridable entity (or in the case of using a boat, the pieces you would get by breaking it).

This is clearly not an intended feature as it is potentially a deal breaker for some people that would like to use this mod.

I'm using the Twitch Launcher to play MC 1.12.2 with forge-14.23.5.2823 and SkylandsMod-0.2.0.jar

2019-03-27-1.log