Bug fixes aside, these are some quality of life changes I'd like to see made to nightblade abilities. Feel free to post your own or discuss those here.
Assassination Tree
Mark Target:
Instead of reducing the target's armor and spell resistance, have this ability simply provide a damage boost against the target for the duration. It's already been said dozens of times that armor reduction abilities do not seem to function in PvE, and the most likely reason is that PvE targets do not have any armor - they're balanced based on hit point limits rather than damage reduction.
Also, I do not think it's necessary to have Mark target negatively effect the nightblade when used. You're not marking yourself.
Lastly, give the mark a visual effect that can be seen by both the nightblade and allied players (and possibly the enemy as well) so that it can be used as a focus fire technique.
Haste:
Make haste effect weapon abilities as well as light and heavy attack speeds. A 30% reduction in the cast time for things like uppercut or snipe would be far more useful than spamming a bunch of light attacks. Currently the only ability this skill has synergy with is siphoning strikes, which isnt even in the same tree.
Shadow Tree
Aspect of Terror:
As a crowd control method, this either needs to effect a larger number of targets, or it needs a longer effective duration. Perhaps change the morphs, causing mass hysteria to instead apply fear to up to 5 targets, and manifestation of terror to only effect a single target but last for 10 seconds.
Summon Shade:
Change the graphic effect on this ability to look like an exact copy of the player that cast it, and have the shade(s) utilize animations from abilities that are slotted on the player's ability bar.
This way the ability would function as a sort of 'mirror image' in pvp, making it more difficult for players to figure out which of the 2-3 enemies they're seeing is actually the player. If necessary, have abilities like magelight reveal the shades to create a counter.
It would also be nice if the shades had some form of taunt for pve use, to allow them to tank a target or two for the nightblade when soloing.
PS4 / NA
M'asad - Khajiit Nightblade - Healer
Pakhet - Khajiit Dragonknight - Tank
Raksha - Khajiit Sorcerer - Stamina DPS
Bastet - Khajiit Templar - Healer
Leonin - Khajiit Warden - Tank