Assassination

One of the favorite tools of the assassin is a pair of daggers coated with vicious poisons. The damage they inflict is deceiving at first—the initial wounds often seem survivable, even superficial. Then the toxins set about their business. Wounds don’t close, and blood loss continues unabated. Assassins begin their work stealthily, choosing their targets and methods of engagement carefully—but once committed to a course of action, they stick to their target until the job is done rather than disappearing into the shadows to avoid their quarry’s blows.

Mutilate

Once per encounter on your turn, you may use your full turn to instantly unleash a devastating attack on an enemy's vulnerable points. Roll one attack: If it hits,  you deal damage with both weapons and reduce the target's attack speed by 1/2. If you crit, you also reduce their AC by 1/2 of your Rogue level (Round down).

Deadly Poison

Starting at 9th level, you become proficient in legendarily deadly poisons made with the mighty Deathbloom flower. Once per long rest, you may coat your weapons in a deadly poison for one hour. Whenever you hit a target, they must make a  CON save = to 8 + your Rogue level. If they succeed, they resist your poison and do not have to make another Con save for this effect for 1d4 rounds. If they fail, they suffer poison damage equal to your Sneak Attack die and gained the Poisoned status. This can only occur to a target once per encounter.

At level 18, the resistance lasts only for 1d2 rounds.

Hemorrhage

Starting at level 13, when you land a precise blow on a target, you rip open a vicious wound on the target's arteries. Every turn (not round) that passes without the target receiving a 15 Medicine check, the target takes 1d4+ your Dex modifier of Bleeding Damage. This damage increases every round the target goes without treatment, to a maximum of 4d4 + Dex a turn. This ability can only affect a target once; after the wound is treated, they cannot be affected by Hemorrhage again. 

 

This ability has no effect on Undead, Constructs, or other creatures that do not concern themselves with Bleeding. Against creatures made up entirely of near-fluid, such as Gelatinous Cubes, Hemorrhage deals d6s instead of d4s.

Vendetta

Starting at 17th level, you can mark an enemy that you can see within 120 feet of you as an objective of your wrath. You become solely fixated on that target, granting yourself advantage on all attacks you make on them. In a  situation where you would normally have advantage, you can instead attack with both weapons while keeping your Bonus Action available.