Mercer is an Assault hero, with the following Leader trait:

Man-At-Arms

Mercer has an X% chance to do Y% of the enemy’s current HP as extra damage (Z% for melee survivors). Additionally, Mercer has a W% chance to resist any status effect.

As a leader, all team members gain these bonuses.

Notes:
• Having other Status resistance properties in combat, such as "Stun resistance" will result in an additional chance of stun taking effect if the first one fails.
• Man-At-Arms can activate on any attack, including Overwatch, Retaliate, Revenge, Punish, attacks from other Leader Traits such as Beat Em Up and Firing Squad, as well as Bodyshots and Charge attacks
• Both the X% chance and Z% chance get boosted by the Lucky trait
• The Status Effect resistance component of the trait works against both walker and human enemy attacks.