Latest server I played had a Perma blind effect around Dark Lord. its very annoying, if you're on the edge you can't see yourself at all, Can't see your buffs.
Is that a custom GRF my server got?... or is that an official change?
It's an official change from ~2014. As long as Dark Lord is visible on your screen, you'll be affected by Blind's visual effect. It doesn't lower your stats though.
You can easily remove it, open monster_size_effect_xxx.lua/lub inside the System folder, search for 1272 and delete the line.