Updates to previous assessment on Charm of Fatigue:
Due to the recent patch, Charm of Fatigue is now VERY viable.
Damage scaling is +1% at 50 Rest, but it scales about 1.5-1.8% ish per 1 drop in Rest, down to 20 Rest. This scaling is not linear, it might be exponential, that's why I couldn't get an exact increase. For example, the damage increase from 43 to 42 Rest seems to be 1.699%.
The damage buff is almost exactly 50% at 20 Rest.
Stamina doesn't start decreasing until 25 Rest and the consequences of not resting have been nerfed insanely.
At 1 Rest I still had 35 Stamina, when my base Max Stamina is 410. Which is more than enough to swing.
At 20 Rest I had around 370 Max Stamina, and I was able to fight the 220 Jana Boss starting at 20 Rest without any issues. There was no need to replenish my stamina at all during the fight, which makes this a straight improvement.
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