Void Warp

Ever noticed how the three dimensions perfectly match up in layers?
In fact, you can perfectly stack the dimensions in the following layers:
Nether, Overworld, End

So why not implement that stacking in the game? Below the void of the
Overworld you will find yourself falling on top of the Nether. Fly high
into the sky and find yourself fighting a particular dragon.

That is all I will tell you without spoilering too much, I suggest you
go discover the features of this pack on your own! However if you do
want to know more:

So what is this actually?

In short: Extreme heights will teleport you to different dimensions.
The Overworld void leads to the Nether roof, the End void to the
Overworld skies. These connections are bi-directional meaning whatever
works one way, works the other. Here's a comprehensive display of all
connections:

• Overworld (Y≤-364) → Nether (Y=400)
• Nether (Y≥500) → Overworld (Y=-114)
• Overworld (Y≥1000) → End (Y=-50)
• End (Y≤-300) → Overworld (Y=800)

Be prepared! You could die when falling into the void!

Important notes

This is not guaranteed to work with custom dimensions. As long as the three vanilla dimensions persist and keep their vanilla names, everything should be fine, otherwise the warps will not work as expected.