• Mage's Fury might be the worst execute ability in the game and it could really use a buff. The least that could be done, in my opinion, is starting the execute scaling at 25% and increasing the damage of the normal hit by ~33% (so that it matches the base damage of Killer's Blade).
• Dark Magic's Exploitation is a worse version of Assassination's Hemorrhage. Both grant a groupwide buff, but Hemorrhage also increases the player's Critical Damage by 10%. I think that it'd be fair if Exploitation gave the player a buff too, especially since Dark Magic is far from overpowered at the moment. Maybe it could increase Direct Damage or critical chance by X% or something?
• I feel like Haunting Curse is lacking a little bit compared to some of the other delayed burst abilities in the game. Maybe the damage could be increased by, say, 10% or it could apply some sort of debuff to the targets?
• When it comes to Blood Magic, I'd still prefer it if casting a Dark Magic ability always increased the player's Magicka or Stamina (instead of having to cast an ability at full health). It's not like the buff is so strong that such a health requirement is necessary, in my opinion, and it'd be nice to just get the extra resources all the time.
• It would be nice for soloing if Summon Storm Atronach's synergy could be activated by the caster too.

Twisting Path
At the moment Twisting Path deals noticeably less damage per second than most class's ground AoE. Since the Major Expedition it grants is only situationally useful, I think the skill would benefit from a damage increase. If both its damage and cost were increased by 10%, I believe it would match Lightning Flood (without that skill's synergy). Twisting Path could then also gain a higher chance to apply the Overcharged status effect, or some other buff, and it still wouldn't be overpowered compared to other skills.

Shadowy Disguise
I think that Minor Protection feels slightly out of place on this morph since it isn’t the tanking morph. Maybe it could get a different buff that is somewhat useful for damage dealers, such as Minor Force or X Offensive Penetration? I do realize that Minor Force is really common and the Penetration might be wasted in a lot of scenarios, but I reckon that either of those buffs would at least benefit some setups.

Born From Shadow
To further increase the viability of Shadow for PvE damage dealers, maybe the damage done to monsters buff could be increased slightly. Maybe from 10% to something like 12%? It would also help if Born From Shadow could be triggered when skills such as Banner Bearer or Shalks are active.

Grim Focus' lost Weapon/ Spell Damage could be added to one of the passives
Since pure Nightblades have lost the Weapon and Spell Damage from Grim Focus and didn’t really gain anything to compensate, I feel like it would be nice if at least some of that W/S Damage would shuffled into the Shadow skill line. It could maybe be added to one of the passives. For example:

• Dark Veil: Increases the duration of your non-invisibility based Shadow abilities by 2 seconds. While a non-invisibility based Shadow skill is active, your Weapon and Spell Damage are increased by 284.

While I believe the skill line is one of the best skill lines for PvP, it's a bit underwhelming for PvE. I really hope the devs can come up with some buffs that increase it's viability in PvE that don't impact the PvP balance too much. I gave it some thought during U47's PTS cycle as well and came up with the following ideas (the first one was inspired by Skinny Cheeks' Warden feedback video, if I remember correctly):

Falcon's Swiftness
Perhaps activating it could give a specific PvE buff - similarly to Born From Shadow? Deceptive Predator could reduce the damage done by monsters by X% and Bird of Prey could increase your damage done to monsters by X%, for example.

Dive (and its morphs)
Due to the long travel time, it doesn't really feel good to use this skill as a spammable. It would be great if its speed would be increased a bit.

Screaming Cliff Racer

• The Weapon and Spell Damage you get when you hit an Off Balance target is obviously good, but that's the only thing the skill has going for it - and it's not enough to warrant using it in optimized subclassed setups. Other spammables are better, and the buff itself isn't good enough to replace a skill such as Tentacular Dread, Grim Focus or Killer's Blade with Screaming Cliff Racer.
• To improve its usage as a spammable, perhaps it could also get an effect similar to Stagger or something? Each hit would then increase your damage done to the target by X per stack, stacking up to Y times.

Cutting Dive

• It's a relatively weak skill when it's used as a DoT and it's also overshadowed by other spammables. But maybe applying Off Balance could be replaced with a more impactful effect?
• I'd personally really like it if the DoT could stack up to X times. Or maybe the instant hit could always apply the Hemorrhaging status effect, similar to how Surprise Attack always procs Sundered?

Growing Swarm

• Since other Class and Scribing skills can apply Minor Vulnerability in an AoE, it's odd that Growing Swarm only inflicts the primary target with the debuff. I think it'd be good if it effected all enemies in its radius instead.
• The 5 meter radius is rather small as well – especially compared to Solar Barrage's 8 meters. It would be nice if it was increased a bit, in my opinion.
• Sadly, Growing Swarm's damage itself is lackluster too. I think it'd be great if it grew in strength over its duration like Hurricane or had an increased chance to apply the Hemorrhaging status effect.

Fetcher Infection

• Even though every second cast dealing 60% more damage, Fetcher Infection's damage is still relatively low and it's not really worth using now that subclassing gives players access to skills that do more damage. Therefore, I think that it would be great if it received some kind of buff.
• Maybe it could infect the target with a debuff that increases their damage taken from Class Abilities (or maybe just Warden abilities) by X%, for example? Something like that would be fitting for the name of this morph, I think, and it could replace the increased damage for every second cast if it would make the skill overpowered.

Subterranean Assault

• I feel like this morph is a bit underwhelming compared to Deep Fissure. Maybe it could always apply the Poisoned status effect, or maybe the damage could simply be increased a little bit?

Passives

• Since this skill line has the most Bleed Damage abilities of all class skill lines, I think adding a Bleed Damage buff (or something that buffs the Hemorrhaging status effect) to its passives would be fitting. (But I wouldn't say no to something else, of course. )
• Since Savage Beast effect isn't that impactful, especially now that different class passives that generate Ultimate don't stack, perhaps it could get such a buff?
• Or maybe it could be added to Advanced Species since other class passives that increase Critical Damage have a second effect as well (see Piercing Spear, Hemorrhage and Fated Fortune for example).

This skill line isn't used much by PvE tanks nor DPS, sadly, as it's overshadowed by other skill lines for both roles. Since the skill line has a couple of cool damage dealing abilities, such as Burning Talons, I'd personally love it if would get some buffs that make the skill line more viable for DPS. Of course it would also have the defensive bonuses, so it shouldn't be as good as e.g. Assassination, but I think that it'd be great if it would be on the same level as Winter's Embrace. I'll list some random ideas below, some of which were inspired by Skinny Cheeks' DK feedback video.

Dragon Leap
It'd be nice if one morph would become better for PvE. Maybe the knockback could be removed from Ferocious Leap, for example, and a strong Flame DoT could be added in its place?

Spiked Armor
I think that it would be great if this skill - or maybe just the Volatile Armor morph - would become more useful for damage dealers, similar to Hurricane. Perhaps the damage could scale off your highest offensive stats or Physical and Spell Resistance? And the damage of Volatile Armor's DoT could be increased?

Dragon Fire Scale
Maybe the duration could be doubled and the “reduced damage taken from projecties” could be removed (or be lowered to something like 10%) in exchange for a new “increasing damage done to monsters by X%” buff?

Deep Breath
While it's a decent skill already, I feel like the damage could be increased a bit without making it overpowered. I believe the damage of the initial hit could even be increased by 33% or something and it'd still be weaker than Blighted Blastbones.
If Deep Breath's cost would be lowered significantly as well, it could even become a skill to build a rotation around (similar to Blastbones).

And perhaps some sort of DPS buff could be added to one (or more) of the passives too.

• Iron Skin - Increases the amount of damage you block by 10% and your Area of Effect damage by 10%.
  Comment: Since Winter's Embrace's Piercing Cold passive increases the amount of damage one can block by 8% and Frost Damage by 15%, I think some sort of DPS buff could definitely be added to Iron Skin.
• Elder Dragon - Increases your Health Recovery by 323 and Weapon and Spell Damage by 108 for each Draconic Power ability slotted.
  Comment: Since Health Recovery is one of the least desirable buffs in the game, this passive also seems like a good candidate for a DPS buff in my opinion.

• I think that the Arcanist's Tentacular Dread costs way too much Magicka compared to other delayed burst skills. It would be nice if it would be decreased to, say, somewhere between 2160 and 2700 Magicka in my opinion.
• The Templar's Purifying Light isn't used much by players. Power of the Light does noticeably more DPS due to the Sundered procs, and Purifying Light's relatively weak Heal over Time isn't enough to really make a difference. Perhaps the heal could be increased or it could always apply Overcharged or something?
• The Templar's Prism and Illuminate passives combined give the same effects as just the Dragonknight's Mountain's Blessing passive. Hence, I believe that it would be fair to add a buff to either Prism or Illuminate.
• Since Major Brutality and Sorcery aren't rare buffs (especially now that most PvE'ers use Tome-Bearer's Inspiration in group content), maybe Molten Weapons could get some kind of other buff as well? It would be thematic if it would add X Flame Damage to your Light and Heavy Attacks, for example, or maybe it could buff Class Abilities by X%.
• Maybe Northern Storm could lose the Major Protection buff and its damage could be buffed instead? The duration of its DoT could be increased and/or Permafrost's guaranteed Chilled application could be moved to Northern Storm. This would make these morphs more distinctive and better suited for different roles.