Killer’s Instinct is a character deck card in Back 4 Blood that is an Offense Type card with Reflex 
Affinity. It gives a significant amount of Weakspot damage bonus at the cost of no longer being able to aim down sights. Killer’s Instinct in Back 4 Blood is a surprising complement to high accuracy builds or melee builds.
Card Ability
+30% Weakspot Damage
Disables: Aim Down Sights
Killer’s Instinct increases Weakspot Damage +30% but players will no longer be able to aim down sights to improve accuracy while shooting.
Pros
This card will be a staple in accuracy-based builds where players choose cards to reach 100% accuracy.
Melee builds that focus on killing Mutations will also benefit from Killer’s Instinct while suffering almost no downside. Melee players can expect to do big damage with Killer’s Instinct equipped with other Melee damage-increasing cards.
Cons
Using the Killer’s Instinct card disables aiming down sights and severely hurts shooting if accuracy cards are used as well. The player will be essentially hip-firing the whole time with the spread as big as the crosshairs on the screen.
Card Synergies
Cards that work well with the Killer’s Instinct card in Back 4 Blood are other cards that disable aim-down sights or other cards that increase Weakspot Damage or general Damage
Hyper-Focused – Hyper-Focused gives 50% Weakspot Damage at the cost of -40% move speed while shooting or using melee. Combined with Killer’s Instinct, a player will have almost twice as much Weakspot Damage.
Quick Kill – This card also disables aiming down sights but gives +50% accuracy to better help reduce bullet spread when hip-firing.