What does the Shadows set actually do? I can’t find any information on it on the Legendex, and the description is kindaa vague. Does it only apply when stealthed??
Which elements work really well with it aside from poison (and Plagued)? Does it work well with Fire (and Crushing Flames)? Thanks!
You go stealth, anyone near gets poisoned. Then the poison debuff has a chance to explode for a percent of its remaining duration left as damage.
This feels like a weird set affix to build around honestly. On very high floors, stealth is usually used for reactive purposes (e.g. to prevent taking fatal damage most of the time) and then this affix wants you to use it in a proactive way, giving anyone near essentially a poison bomb. This is prolly a PvP designed set affix IMO but if you can make it work in PvE, ill be curious to know whats your build 
I have seen people use Crushing Flames with Frozen and they have claimed it works, maybe Frozen can be used with Shadows if you want to try it out but you need ways to get your enemies frozen(ice debuff) first before Frozen(set affix) explosion works.
I tried brewing with Shadow set affix and I found that “going stealth poisons enemies” does not work. Poisoning an enemy in other ways however will still trigger the “detonate” part of the affix. The Shadow + Frozen combo works fine but really needs a swarm for the combo to work and is less effective as the enemies get tougher and tougher, prolly need crushing blows on very high stage.
I’ve thought it worked without stealth as well, the stealth being optional to build with.
actually, the one time i used/tested Shadows, i used Stealth to cast a Poison attack that was centered on my Wizard (his other Gears were my Floor Climbing ones), and since it wrecked my ability to do damage while poising a lot of enemies (was on a pack size map), my screen froze 
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on the other hand, it other attacks can make use of the Shadows special ability with Poison attacks, that sounds pretty powerful indeed 
!