So I'll get straight to the point, I'm playing on a certain wow server, using a TC2 emulator (Surprise right?), anyway about 15 months ago I played on Chaos Crusade until it was mutilated by blizzard, I actually stayed on the server when it changed host and those who took care of the CC DB used a mangos emulator, possibly a repack.
But the point is, their emulator's vanish would make you immune to projectiles that were in the air when you vanished, meaning that it works the way it does on retail (Minus a few abilities such as charge, blind, cheap shot, hammer of justice etc etc).
I'm currently trying to find that core / repack to get a friend of mine to look into it (I don't know much about these things myself). I want my friend to look into it so that he might make it work for tc2 servers.
Anyway, I'm asking for your help to find one, possibly someone of you guys plays on this repack / core and could help me narrow down my search.
Vanish is currently bugged in the base TC2 core pretty badly. (Vanish buff not dropping when Stealth buff drops, Vanish buff being a stealth effect?) I'm sure you could test some of the patches posted in the issue tracker on the TC2 google code, however, scripting the "immunity" Vanish gives seems impossible (even to Blizzard), so it may or may not be awhile. As you can see, the issue was posted many times on their issues tracker. ;P