So. Invisibility. Let’s get this out of the way.
More often than not, misinformation about Invisibility is quoted pretty much everywhere, including by yours truly.
*Warning: The following post contains math, although not a lot of it*
Invisibility reduces threat by 10% every second for five seconds. This does NOT mean that over the course of five seconds, threat is reduced by 50%. Rather, this 10% threat reduction takes place every second, separate from the other reduction.
In other words, relative to the initial threat you had, the first tick reduces that threat by 10%, the second by 19%, the third by 27.1%, the fourth by 34.4%, and the final tick by 41%.
In a practical sense, let’s say you have 10,000 threat when you pop Invisibility.
The first tick will reduce your threat by 1000, leaving you with 9000 threat.
The second tick will reduce your threat by 900, leaving you with 8100 threat.
The third tick reduces your threat by 810, leaving you with 7290 threat.
Tick #4 reduces threat by 729, leaving you with 6561 threat.
The fifth and final tick will reduce your threat by 656. Leaving you with 5905 threat total.
So it isn’t half your threat; it’s just over 40%.
If you allow Invisibility to run it’s course all the way to you becoming completely invisible, it will drop you from combat, thus completely clearing you from the threat list. In other words, a 100% threat wipe. This threat wipe is caused not by the fact that you are invisible, but by the fact that you have removed yourself from combat.
One notable exception.
Against raid bosses (I’m talking the big guys like Gruul’s and Archimonde, not things like Heroic dungeon bosses) you can only leave combat three ways: killing the boss, being killed, or zoning out of the instance/reaching the boss’ “tether”.
Invisibility does NOT drop you from combat in this type of situation, and thus you are NOT dropped completely from the threat list. You merely get the 41% reduction and cease to contribute to your own threat.
Hope this clears things up.