A neat little mod to turn The Wither the guardian of The Nether as a required boss fight to unlock it and all its features.
Here's a cool showcase, works better than words:
I always felt The Wither was too cool to be optional and forgotten, I also always felt The Nether was too easy to access for how much it offers. So why not kill two birds with one stone while adding some cool visuals? So I did!
I was surprised I couldn't find a mod that already did this, lots of modpacks seal the nether in other ways, but why not use something already underused in the game? I could use it for my modpacks and I hope all of you can now.
Advancements
I took the chance to add some advancements, inspired by a few old achievements 
Summoning The Wither through the ritual will grant the advancement "Withering Heights" from vanilla, defeating and unlocking The Nether will unlock the two new advancements "The Beginning?" and "The Beginning."
Gamerules
There is some light config for the mod in the form of gamerules!
netherlockConsumeStar
Consumes The Nether Star to unlock The Nether.
netherlockPeaceful
Automatically unlocks The Nether while playing on Peaceful difficulty.
netherlockRitual
Whether The Wither is summoned through the ritual sequence instead of instantly.
netherlockWarning
Whether the first portal attempt warns the player before beginning the ritual.
Commands
A simple mod command to lock or unlock The Nether immediately
/NetherLock'd lock/unlock
Thank you!
The mod is fairly simple, so I have short-term plans to make a 1.20.1 and a Fabric version. I am open for any suggestions for features, configs, commands or anything similar! (I was actually considering adding a way to re-lock The Nether but couldn't think of one) So I would love to read your comments!