Best Unique Features You've Seen?

[crysiscore3]

Thought this might be interesting. I've tried a LOT of Ro servers over the years, and it seems most of them have at least a few unique things(I'm not talking about hats/cards).
Some of them have been great ideas, and something I wish I would see more often.

Here's my list:
NPCs:
NPC where you can check ANY item's description.
Job changer that allows you to change your job to anything, at any time.
Alternative Kafra girls. All cute anime style. Rather than the matronly things I've seen everywhere other than AERO.

EXP:
We had a max level of 255. But after you hit level 235, you no longer gained exp from monsters. The only way to hit 255 was WoE. Each time you were in a castle with your guild upon a break, you'd gain about 3 levels. You got 5 if in the castle and possessing it upon WoE end.

PK server:
When killing someone more than 20 levels below you it would activate Nightmare mode for an amount of time, depending on the level difference between you and the one you killed. If a 99 level player killed a level 15 player for instance, nightmare mode would be enabled for 30 minutes(or until another player killed you), and it was a status effect(logging out for 30 minutes wouldn't cause it to go away). There was a visual effect that all players could see when you were in the nightmare mode.

Items:
Yggdrasil Berries with a %0.5 chance of coma. No buff or item could prevent it. - High rate server.

[Relics]

Best unique features I've seen that were actually good..
note this was in 2005-2006

Guild buffs worked in PvP, allowing pure FO champs to be viable
Soulbreak formula included off-hand weapon/upgrade/card damage, no soullink/edp was scarce at the time making SBK sinxes viable

then some other server I played on had some nifty quirks
Ygg couldn't be spammed, had a 2 second delay
Soullink cost an edp bottle

[Triper]

Custom Dungeon called The Void that made people party like madness, never seen anyone party like that before with no effort, really really good at a low rate which name I don't remember and was sad after the server ended by corruption ):

WorstBest Anti-Bot System Ever that was based on adding a GIGANTIC[yes, it was huge to the point that me playing on 1280x900 got the screen full covered with that npc image custom made] Image to your screen when you would log in game and tell you to input 4 numbers[if you would misclick at the pic, bad luck, alt+f4 and try again lol] from a High Rate which name I don't remember.

Custom BG from eAmod. Damn, BG without that isn't that awesome as with.

Dyna Headgears - a donate headgear that people can use and transform it into any ro headgear

[Ace]

This happened around 2009-2010

For me, the best features I have ever seen was the "Achievement System"

After achieving 1 achievement, player will get rewards.

Also the "Weapon Level System"

You cannot wear a level 4 weapon (example: Balmung) If you cannot level your weapon from 0 - 4 That was very challenging...

[MySassyAssy]

Back on qualityRO...

-1 arrow use
-Donator's Room
-Level 90 trans without rebirth
-Low chance of spawning MVPs with DBs
-Fun Survival Events

Others:

-VisionRO's manual/guide thing
-eternityRO's customized bg