5e: Killer Feats for Contract Killers with Killer Smiles

The following feats are perfect for assassins and spies who want to be ready to tackle a dirty job, no matter how secure the facility or public the environs. These new tools give such characters new ways to enveigle secrets from their marks and to keep them alive in the event they become exposed.

Blade in the Dark

You are a master of up close and personal wetwork, silencing guards and targets with lethal efficiency without drawing unwanted attention. You gain the following benefits: 

• Increase your Dexterity score by 1, to a maximum of 20.
• You gain proficiency in Stealth. 
• When you hit an unsuspecting or surprised creature with a finesse weapon, roll 2d6 and add it to the attack's damage. Your Blade in the Dark damage bonus stacks with a Rogue's Sneak Attack class feature. 
• If you reduce an enemy to 0 hit points or render them unconscious while they are unaware or surprised, you muffle their mouth or otherwise prevent them from making noise. 

Concealed Weapons

You are a contract killer who has mastered the art of eliminating targets when others would find it impossible, too risky, or too public to reach them. As such, you perfect new skills that enable you to smuggle implements of death into environments as varied as ballrooms and secure facilities. You gain the following benefits:

• Increase your Dexterity score by 1, to a maximum of 20.   
• You are proficient with underhand weapons and always carry several of them on your person. Underhand weapons are creative killing tools that easily blend in with your outfit and can be use as both garottes and whip-like lashes. Common techniques for creating underhand weapons include: sewing razor blades into scarves, sashes, or along the edge of belts; replacing necklace strings with durable wire; and forging decorative belly chains that are in fact strong enough to choke a person without breaking.
  
  You can always draw an underhand weapon while you are wearing your own clothes. You can make the necessary modifications to a set of clothes that has been borrowed or stolen by spending at least an hour incorporating existing underhand weapons into the outfit and creating new ones that better suit it.
  
  In your hands an underhand weapon is a two-handed finesse melee weapon which deals 1d6 damage, and because you carry so many you can choose whether it deals bludgeoning, piercing, or slashing damage when you draw the weapon from your outfit. Wielded by someone without this feat, an underhand weapon is also considered an improvised weapon (and therefore deals only 1d4 damage), and its damage type must be predetermined. 
• Your underhand weapons and one other small or otherwise easily hidden item are concealed so well on your person that anyone observing or searching you has difficulty finding them. The item in question can be a dagger, light hammer, sling (with up to 10 sling bullets), whip, blowgun (with up to 30 needles), or a similarly sized item that weighs no more than 5 lb.
  
  Your underhand weapons and the concealed item are hidden so well that they cannot be spotted using Wisdom (Perception). When you are searched, the searcher rolls their Intelligence (Investigation) check as though they had disadvantage, using the lower of the two results for the purposes of finding these items and the higher of the two results for the purposes of finding any other objects or secrets you are trying to hide. If the searcher has advance knowledge that tells them where and what they are looking for, they roll their Intelligence (Investigation) check normally.

Consummate Liar

Falsehoods pass through your lips as naturally as breath through your lungs. You gain the following benefits:

• Increase your Charisma score by 1, to a maximum of 20.
• When you make a Charisma (Deception) check, the minimum you can roll on the d20 is 8. If you roll less than that, treat your roll as an 8 instead. 
• If you have already successfully lied to a creature since your last short rest, you have advantage on all further attempts to convince that creature of a lie until you fail an ability check, you tell a lie that is demonstrably false, or you take a short rest. Once you are caught in a lie, you cannot gain this benefit against a creature that knows you lied until at least 24 hours have passed.  

Devastating Allure

You possess great physical beauty and potent animal magnetism, which you use to manipulate those who are attracted to your sex. You gain the following benefits: 

• Increase your Charisma score by 1, to a maximum of 20.
• Any Indifferent NPC who considers you attractive is instead Friendly towards you (though not your allies).
• You have advantage on Charisma (Deception) and Charisma (Persuasion) checks made against anyone whom is attracted to members of your sex.
• You add +5 to the result of a Charisma (Performance) check against any member of the audience who is attracted to your sex.
• Whenever you deal psychic damage to any target whom is attracted to members of your sex, increase the damage by 1d4.

Note that when an NPC's preference has not been predetermined, the DM may choose to do so randomly using any method of their preferencce. While an oversimplification of the demographics of sexuality, here is one possible method rolled on a d12: 

1-3: attraction to the opposite sex (heterosexual).
4-5: attraction to the male and female sexes (bisexual).
6: attraction to all genders (pansexual).
7: attraction to multiple genders, but not all (polysexual).
8: attraction to non-binary persons (skoliosexual).
9: not attracted to anyone (asexual).
10-12: attracted to the same sex (homosexual).

Knife Thrower

You have mastered throwing knives. You gain the following benefits:

• In your hands, light thrown weapons have a range of 30/90. 
• When you make an Attack action and all the attacks you make are with daggers, you may make one extra attack which must also be with a dagger. If you are a monk, this attack deals normal damage for a dagger rather than your Martial Arts damage. 
• You may spend your action to aim at a target you specify. If you do so, add +5 to all attack rolls made with thrown daggers on your next turn. 

Other Feats for your Build

You'll definitely want the Skulker feat both for its stealth abilities and so you can avoid the disadvantage from operating in dim lighting conditions. Actor can help you get into private parties and other places you don't belong. Consider Mobile to more quickly maneuver through an enemy facility or flee it if things go South. Lucky is a solid choice for someone who takes so many risks! If building a spy rather than an assassin, consider Observant.