20-hour Yumcax fight due to unbreakable regen shield

Platform: Windows
ISP: ATT Uverse
Type of Internet Connection: Wireless
Internet Connection Speed: 54Mbps
Date & Time: July 22
Frequency: All day
Character Name: Edyth
Race: HumeF
World: Quetzalcoatl
Main Job: COR Lv.99
Support Job: WHM
Area and Coordinates: Yorcia Weald Wildskeeper Reive
Party or Solo: Solo and in Alliance
NPC Name: None
Monster Name: Yumcax
Steps:
1. Get Yumcax down to 30-something % HP so that he puts up the regen shield. (I wasn't present when this occurred.)
2. Slow down damage so that the regen effect is faster than damage dealt. (I wasn't present when this occurred.)
3. Once Yumcax regens up to a certain HP threshold, his shield can no longer be broken by wind magic damage. He went up to about 90% HP, then down to 50% HP before we were MPKed too many times by panopts and people gave up and left, and then he got up to over 70% HP before I finally gave up and left.

Best performed on an underpopulated server with people who like to MPK using Yumcax's Watchmen so that the unbreakable regen shield for the entire battle is entirely insurmountable.

I have been in this fight for almost 11 hours myself, and it is hideous. I was there for part of the time that Edyth was, and everything she says is true. This is currently turning into Pandemonium Warden v 2.0, as the fight has now been going on for 24 hrs.