Ebon Piercer Omega Tank

This build uses Wither to its fullest extent by stacking absurd amounts of Intelligence to get insane damage over time. But not only is it doing an incredible amount of damage, its also extremely tanky thanks to Osseous Gale keeping 100% uptime on Bone Storm and Necrotic Carapace keeping us fortified at all times.
Ebonpiercer is by far the best Shadow has ever been. So if you've been looking for a good one, this is it.

1. Keep up Decrepify
2. Use Corpse Tendrils to keep enemies grouped.
3. Use Blight as much as possible to apply Ebonpiercer and stack the Blighted aspect.
4. Use Blood Mist as needed to dodge enemy attacks, especially against bosses.

This build thrives off intelligence because the entire goal is to stack the Wither paragon node as much as possible because its scaling is just insane. And this season we can get more intelligence than ever before. Masterworking, Greater affixes, and the itemization changes really pushed how far Damage Over Time builds can go and this is the pinnacle of that, so its VERY important that you stack as much intelligence in every piece of gear that you can.

Attack Speed likewise also ends up being a very important stat because it directly impacts how much damage over time you're able to get out. This build thrives when it can just sit there against an enemy and spam endlessly thanks to the essence per second rolls in our armor. But the more attack speed we have, the more essence per second rolls we need. So make sure you to keep a balance of those two stats.

Against bosses the main goal is to your Blighted Aspect stacked as you stagger the boss, which is going to turn on things like the Control glyph as well as Concussive Strikes and also give you a clear window to safely stack your damage over time without fear of having to dodge attacks. These stagger windows are where you're going to see a majority of your damage to make sure to use these windows well to have the best results when bossing.

Essence Management and Additional Information

Make sure to be casting Blighted Corpse Explosion during fights as it will not only help with essence generation in combination with the essence per second, but it also is used to turn on damage multipliers like Flesh Eater and Fueled by Death.

A higher damage build can be used by replacing Osseous Gale with the Retribution Aspect. The reason why this can be very strong is because Retribution will be applied twice (also known as 'double dipping) against a staggered boss for a x40 multiplier. And while the damage from it is substantial, its less consistent than getting 100% uptime on Osseous Gale. But If you're up for the challenge its definitely worth considering.

Likewise there's also other things about this build that benefit from this 'double dipping' mechanic. Tempers and affixes such as "damage%", "damage over time" and "darkness skill damage" all will double dip, so its very important you pick these up as tempers or affixes wherever you can.

And lastly, I wanted to highlight why we're opting to use Topaz in the armor instead of Rubies like you'd normally see in builds. Because of how extreme the Wither scaling is for your damage, the damage gain from these Topaz is astronomical; They were buffed in season 4 to give 100 Intelligence each, which equates to 8 entire Wither breakpoints which is insane.