The new Assassin skill tree introduces a way to heal on kills with 0 armor. This guide lists out all the skills that can help extend this simple interaction into a somewhat meaningful way to mitigate damage in loud heists.

The general idea:

• Assassin't Mettle allows you to heal 10 HP every marked enemy silencer kills with 0 armor.
  
• Having a silenced weapon and a consistent way to mark enemies is a must.
  
• Healing beyond max health also generates Adrenaline.
  
• Overheal by stacking Adrenaline from Assassin't Mettle.
  
• This skill is best utilized at an enemy spawn point, or a choke point to hold off of.
  
• Best used with Smoke Grenade, Standard Lining armor, and a weapon with silencers.

The main part of this build

• [Assassin]
  
  • "Basic" (Good source for RUSH)
    
  • "Assassin's Mettle" (10 HP heal)

Greatly enhances the way this build works

• [Scrambler]
  
  • "Signal Scan" (ECM marking sniper, techies, FBI vehicle)
  
  
• [Assassin]
  
  • "Death Knell" (Enables marking with throwables)

Other skills that work well with, but not required
Smoke is recommended for its range and duration compared to other options.

• [Ammo Specialist]
  
  • "Aced" (Good EDGE source when resupplying throwables with Ammo Specialist - Scrounger)
    
  • "Scrounger" (10% resupply is unreliable & requires EDGE)
    
  • "Top Up" (Extra resupply per ammo box use)
  
  
• [Inflitrator]
  
  • "Frugal Thrower" (20% resupply is less unreliable)
  
  
• [Demolitionist]
  
  • "Overcooked" (Negates fuse time, good for aggressive playstyle)
    
  • "Extra munitions" (Pairs well with Ammo Specialist - Top Up, bigger reserve means more throwables between resupplies)
  
  
• [Tactician]
  
  • "Aced" (Increases marking range of smoke/stun/shock)
    
  • "Discombobulate" (Damage debuff)

Medic Bag, First Aid Kits provides healing outside of Assassin - Assassin's mettle

• [Medic]
  
  • "Steady hands" (Extra healing from Medic Bag)
    
  • "Triage" (Extra healing from Medic Bag & First Aid Kits)
    
  • "Field Surgery" (Extra healing from Medic Bag)
  
  
• [Manipulator]
  
  • "Menacing" (Enables trading Law Enforcements for First Aid Kits & Armor Repair Kit)
  
  
• [Fortitude]
  
  • "Supraphysiological" (Extra Adrenaline gains)
    
  • "Walking Tall" (Slows Adrenaline decay)

If one-shot is unachievable consider damage buffs for lower TTK, or simply switch to a weapon that's capable of

• [Ammo Specialist]
  
  • "High Grain" (Damage buff, requires ammo bag)
  
  
• [Mower]
  
  • "Basic" (Good EDGE source with high RPM weapons)
    
  • "Replenish" (Ranged ammo box pick up)
    
  • "Sprint Loaded" (Less down time when finding cover)
  
  
• [Enforcer]
  
  • "Basic" (Good GRIT source when played aggressive or on choke points)
  
  
• [Strategist]
  
  • "Combat Marking" (Requires EDGE, damage buff)
    
  • "Threat Assessment" (Requires GRIT, defense buff)
    
  • "Misdirect" (Requires RUSH, dodge buff, easily achievable with Assassin - Basic)
  
  
• [Assassin]
  
  • "Killer Kinesthetics" (Extends marking on kill)

• You can also mark drones and benefit from drone kills if they are marked.
  
• Running out of throwables means no SWAT markings, either find a way to resupply throwables or play safe if you can't consistently mark enemies other than specials