Firstly #removevoidform
Here’s blizzards reason for adding the spell:
Returning Ability: Devouring Plague
We’ve seen a lot of feedback that Void Form can be challenging to utilize to its full potential in some combat situations, such as in Mythic Keystone dungeons on non-boss encounters, or for leveling and doing outdoor content. We tend to agree that Void Form can feel unrewarding in situations where it becomes difficult to maintain efficient insanity generation. Rather than heavily re-designing Void Form, we’re introducing a new tool for these combat situations with the return of Devouring Plague.
Along with Void Eruption, Devouring Plague will be the only other spell that costs Insanity. Our intent with Devouring Plague is for it to be used on enemies who die quickly, such as common creatures while leveling, or on simple trash pulls, while Void Form is more powerful on longer combat encounters.
Datamined on wowhead:
Devouring Plague: Afflicts the target with a disease that instantly causes (72.6% of Spell power) Shadow damage plus an additional (50% of Spell power) Shadow damage over 12 sec. Damage caused by the Devouring Plague heals the caster.
Shadow Word Pain for damage comparison:
Shadow Word Pain: A word of darkness that causes (16.5% of Spell power) Shadow damage instantly, and an additional (99.2% of Spell power) Shadow damage over 16 sec.
First impression is that the damage of DP is too low and the duration far too long for the insanity cost and what blizzard says the spell is meant for.
Void Eruption deals much more initial damage to all targets within 10yds, while only costing 10 more insanity with Legacy of the Void, also giving access to Void Bolt which deals almost the same damage as Devouring Plagues initial damage plus DoT combined.
What this means to me is that Voidform is still better to get into first and then bolting at least once before using DP (maybe even mind blast before it also) on short duration single target fights. Most likely to be used right before a target hits execute range.
As we get more stats we might be trying to weave a few DP’s into low stacks voidform on longer fights, this will make maintaining voidform even worse and I hate even thinking about it.
Along with Void Eruption, Devouring Plague will be the only other spell that costs Insanity.
This is just wrong, Void Eruption doesn’t ‘cost’ insanity, it only requires it. Devouring Plague will be the first ability that actually subtracts insanity outside of voidforms ramping decay.
This will really mess with our aoe rotation if the numbers work out, it could be potentially better to cast Void Eruption then immediately DP to drop VF, then mind sear back to 60 then repeat. If it works out that just spamming mind sear is better then I don’t see DP being used in aoe situations.
As for pvp I think DP will be a nice addition for certain situations, especially with the heal.
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To summarize I think the addition of Devouring Plague without fixing any of the fundamental problems of voidform is like giving a prosthetic arm to a person with no legs. Borrowed power has been our wheelchair since the start of Legion and with it all gone we either need more borrowed power or an actual rework.
How to actually fix shadow? My suggestions here: A Proper Rework for Shadow is Needed, and my suggestions