Use vertical connecting portals to "stack" the dimensions.
You can see the "Dimension Stack" button when creating a new world.
If enabled, the bottom dimension will connect to the top dimension, creating a vertical world wrapping.
If no dimension is flipped, this option will have no effect. The gravity changing functionality requires Gravity Changer (Gravity API) mod.
This option can be either "Relative to World" or "Relative to View".
If it's relative to world, the dimension connecting portal won't change your gravity. When entering a flipped dimension, your gravity relative to the world will not change but the "viewing gravity" will change and a rotation animation will perform. For example, if your gravity is downwards before, then after going into a flipped dimension your gravity will still be the same as the direction that water and lava flows down.
If it's relative to view, the dimension connecting portal will change your gravity. The "viewing gravity" will not change and it will not perform rotation animation. For example, if your gravity is downwards before, entering a flipped dimension will make your gravity upwards, which is the opposite of the direction that water and lava flows down, but you will see no "view rotation".
It's sometimes confusing that not changing the view gravity means changing the gravity relative to world, and not changing the gravity relative to world means changing the view gravity.
By clicking "Edit" you can edit the selected dimension entry's options:
This controls the generated portals' scale transformation. The generated connecting portal won't change the crossing entity's scale.
If you want that one block in nether corresponds to 8 blocks in overworld, set the overworld's scale to 8.
It's recommended to either (1) set the scale between overworld and nether to be 8 or (2) set the nether portal mode to be
disabled. Because dimension stack does not interfere with how nether portals work, if dimension stack allows player to travel between overworld and nether with 1 by 1 space ratio, and nether portal allows travelling with 1 by 8 space ratio, then the player can easily reach the world border by using two travel methods alternately.
Controls the portals' rotating transformation. If enabled, makes the dimension looks "flipped". Does not change the gravity direction in that dimension (unless you enable gravity change option). If a flipped dimension connects to a non-flipped dimension, the connecting portal will have a 180 degrees rotation transformation along X axis.
Controls the portals' rotating transformation. Make the dimension looks rotated along Y axis.
Specify the bottom and top Y level of the portal. You can left these two empty by default.
If Bottom Y is left empty, it will use the dimension type's
min_y property. If Top Y is left empty, it will use the dimension type's
Specify a block that the bedrock will be replaced into. If empty, the bedrock will not be replaced.
Re-configure Dimension Stack Using the Command
This mod has command
/portal dimension_stack (since MC 1.18) that allows re-configuring dimension stack when the world was already created.
How to Use Dimension Stack on a Server
The first method: create a dimension stack world on client and then copy it to the server.
The second method: use command
/portal dimension_stack to enable dimension stack on the server and manually replace existing bedrock blocks into obsidian.