Upside Down Add-on
Do you want a different survival experience? There are lots of cool different survival maps, but do you want to experience something completely new? Here is an add-on that modifies existing worlds. (Windows 10 PC only currently)
▓ Windows 10(PC) only ▓
▓ Turn on "Caves and Cliffs" ▓
▓ Turn on "Additional Modding Capabilities" ▓
▓ Turn on "Activate Cheats" ▓
▓ It's destructive ▓ Please backup your world ▓
It will move every block and every entity (in the overworld) from Y=191~-64 to Y=64~319. The distance depends on "Simulation Distance".

This add-on isn't adding anything or replacing anything so it should not conflict with any other add-ons.
Support multiplayer.

Have fun!
0.0.9 :
Special optimization solution.
"Caves and Cliffs" only.
More chunks will now be flipped.
Installation
▒Look into the ZIP file! The MCPACK is inside▒
Turn on "Caves and Cliffs"
Turn on "Additional Modding Capabilities"
Turn on "Activate Cheats"
Windows 10(PC) only
Checksums:
Upside Down_0.0.9.mcpack
MD5: 333BCE4D90E04EF40BC19E7317E5B0DA
SHA1: 6FA73DBFE654C6396ACBAD2A79610E9D5E0BABAB
SHA256: 35ACCE68072494C8338E701D80F092BDB93051BECB0889D82297E885CF2E5BE6
creator: https://twitter.com/Worldwidebrine/