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Can you guys elaborate on this maybe?
Threat reduction, even when it states it is for all sources, does not actually apply to all sources of damage. Early in the introduction of imbues, there was much guesswork. One of those guesses was that negative threat rolled over after -100 so that anything beyond that was actually generating again. Very few actually did detailed testing, but some did.
I was one who did detailed testing, knowing how much threat a tank created with a single intimidate and not doing anything else to generate more, then with -100% reduction, and with more, doing basic damage only with no extras to ensure it worked as a baseline (exceeding the effective intim threat in damage by 2 orders of magnitude so as to eliminate the possibility of 99% reduction instead of 100%), then resetting the instance to eliminate any contamination, and one by one adding other sources back in to see how each worked, with a reset between each new source, and keeping track of damage vs intim effective threat to see if/when aggro would be stolen, etc, etc, etc.
I did not notice any rollover when past -100% threat.
Threat reduction works fully on base damage.
Threat reduction works fully on sneak attack damage.
Threat reduction works fully on special attacks that do/multiply base damage
Threat reduction does not seem to apply at all to imbues.
Threat reduction does not seem to apply at all to extra damage procs from ED stances like Prism
Threat reduction does not seem to apply at all to extra damage or procs from epic moments like Inexorable Advance.
Threat reduction does not seem to apply at all to extra weapon damage such as Holy +6d6 good, etc.
Threat reduction does not seem to apply at all to extra damage from special attacks.
Threat reduction does not seem to apply at all to item procs (dripping with magma, etc)
Thus even with -100% or more negative threat, builds with lots of imbue dice, and/or during bursts with epic moments in full swing, still generate threat and can potentially pull aggro.
My initial testing was done over a year ago, and I spent a few hours doing it, yet still didn't test every possible scenario. I have not noticed any major changes since then, but that doesn't mean there haven't been any (sometimes things change and are not mentioned in release notes). Because doing tests like this can take so long to do, so I'm not inclined to re-test unless/until some major changes happen.