Hi. I have a question regarding the "world tier" system. It seems odd to me that after progressing to a higher tier, it's still possible to revert back to a previous one. I believe it would be fair to prevent players from lowering the difficulty once they've advanced to a higher tier.

This current setup allows players to abuse the system — for example, by farming high-tier mobs for powerful gems or items, and then switching back to a safer tier afterward. Is there any way to disable reverting to a previous tier? If not, maybe it’s something worth considering?

As an alternative, perhaps reverting to a lower tier could be automatic (or optional) after a death (or multiple deaths) — from an affix boss.
I'm just not sure how to deal with this kind of abuse on the server. I'd really like to encourage players to progress through the mod in a fair and honest way.

That is not "abuse".

You receive drops according to the tier. It is intentional you can return to a lower tier if you want to relax.

This is a sandbox game, after all.

In general the difficulty with a locking system is the "how" - I figure most people who might ask for one might have different designs for how the tiers are awarded.

The easiest would be a "disable manual tier switching" config and let the pack author figure out how to enable them (command advancement reward could work?)

I agree with your point about the sandbox game.

Still, I think it would be nice to have an optional setting to prevent switching between difficulty tiers freely. Maybe I’m wrong, but this mod seems to introduce a more “hardcore” element to the game, and being able to instantly drop from a challenging tier to a peaceful one kind of takes away from that hardcore feeling.

It’s a bit like being deep in a cave, getting overwhelmed by mobs, and then just switching to Peaceful difficulty to make them all vanish. In vanilla Minecraft, there’s an option to lock the difficulty, so even if a player is tempted, they can’t change it mid-game.
If there were something similar in this mod, I think that would be fantastic.

Yes, it would be great to disable manual tier selection — as far as I understand, there's currently no way to do that.
Automatically assigning tiers based on some kind of advancement sounds like a solid idea.

I remember in earlier versions of the mod, even at the start of the game, bosses could spawn that would one-shot me in diamond armor 😄 — that kind of danger added a lot of charm to the experience.