1st of all, skill can only take effect if its cast before mobs spawn as observed through mob speed and stat reduction
[SPOILER="Affect on walking speed"]
Pre-cast
[video=youtube;4onHX3--QAE]http://www.youtube.com/watch?v=4onHX3--QAE[/video]
Pos-cast
[video=youtube;6rqViIyL4SI]http://www.youtube.com/watch?v=6rqViIyL4SI[/video]
I also tried to cast it on top of mobs to obtain the same result of no speed reduction. The vids also show how bad the speed reduction is lol.
[/SPOILER]
Stat wise the skill does what's intended and reduces 30% of the mob stats (tests made on golden bone lancers on gop elite)
normal
[Image: http://puu.sh/6hQ6N.jpg]
under sorrow sonata
[Image: http://puu.sh/6hQai.jpg]
However str/max deduction doesn't match. Considering mobs lose 48 str (160x30%=112 // 48 loss) they should've lost 20 max and not 60 as observed.
Considering a possible hidden effect on the skill i went ahead and tried it on myself.
normal
[Image: http://puu.sh/6hQiE.jpg]
excuse my shitty dual wield
under sorrow sonata
[Image: http://puu.sh/6hQkV.jpg]
Back to the deduction formula, i am losing 270.9 str (108.36 max) which matches perfectly my stats
To conclude,
>either chorus have a hidden max debuff on mobs OR...
>mobs take their melee damage from more than just str (doesn't match anyway) OR...
>str/max formula for mobs isn't the same as ours (2.5str / 1 max)