Nether Under Overworld

Details: This datapack/server-side mod allows you to cross the bedrock barrier between the overworld and nether. Standing on bedrock at the bottom of the overworld will teleport you to the same x/z coordinates in the upper layers of the nether, and touching your head against the bedrock at the top of the nether will teleport you to the same x/z coordinates at the bottom of the overworld.

If you are in adventure or survival mode, the teleportation process will create an air pocket at your destination. If you are in creative or spectator mode, you will still teleport, but an air pocket won't be made so that the world isn't affected by operators or spectating players.

Compatibility: Nether Under Overworld is designed to be paired with something like the No Portals mod that disables the usage of nether portals, as otherwise this can be abused to travel long distances by leveraging the 8:1 scaling between the two dimensions. Since Nether Under Overworld doesn't affect the x/z coordinate when teleporting, this puts the two dimensions on a 1:1 scaling.

While the Immersive Portals dimension stacking feature is amazing and connects the two dimensions seamlessly, the mod is required on both the client and server, is performance heavy, and incompatible with a few others that I enjoy, so I decided to make Nether Under Overworld as a budget replacement.

Furthermore, there are two versions of Nether Under Overworld: one for vanilla nethers that are 128 blocks tall, and one for those with a 256 block tall Amplified Nether. For those using Incendium and other datapacks that change the nether height to something that isn't 128 or 256, you will need to shift the values in the nuo:top_nether predicate and the nuo:teleport/nether function accordingly.

Uninstalling: Nether Under Overworld can be uninstalled and reinstalled whenever you'd like.