Mercy Kills Warframe allow you to instantly assassinate a target that has lost 5% of its health. If you have a build that uses impact damage, it can increase the chance of being able to mercy kill at a higher percentage of their health by 10% for each stack of impact damage.
You'll know when you can perform a mercy kill because a red symbol, shown in the image above, will appear above the enemy's head. You can then interact with them using the onscreen button to perform the kill. The Mercy Kills extended the animations, much longer than the average finisher.
Mercies are performed with your Parazon, a Tenno multi-tool that all Warframes wear on their wrist. The Parazon can also be used to hack, kill Kuva Liches and Kuva Thralls or Larvlings. Any of these attacks, except the Kuva Lich, will count as a mercy kill for a Nightwave challenge.
The reason for doing Mercies instead of Finishers comes down to the mods you can equip on your Parazon. Performing Mercy Kills with certain mods attached will leave stat and gameplay benefits that you don't get from Finishers.
These mods can be found by killing bosses and will give you the perks below.
- Blood for Life: 50% chance to create a Life Orb at Mercy.
- Blood for Energy: 50% chance to create an Energy Orb on Mercy.
- Blood for Ammo: Mercy reloads magazine by 100%
- Hit and Rune: On Mercy: + 60% parkour speed for 6 seconds
- Out Of Sight: Blind Enemies 18 yards from the 'Mercy' kill.
