Butterfly is a trait in Destiny 2 that can appear on 12 weapons. There is also an enhanced version with a stronger effect.
What Butterfly does
Aiming this weapon for a short period without firing causes your target to explode the next time you deal final blows. Timer resets when you stop aiming down sights.
Enhanced version
Aiming this weapon for a short period without firing causes your target to explode the next time you deal final blows. Timer resets when you stop aiming down sights.