Is Mercy's damage boost applied on fire or on hit?

The information in this answer previously were based on testing from Closed and Open Beta. It has now been deleted due to new testing from other players in the community.

Mercy's damage boost is applied on hit.

However....

Mercy's damage boost needs to be toggled on the player when the enemy receives the hit. Meaning, it's fine if the projectile isn't boosted when it launches, but by the time it gets to the enemy the Mercy must be boosting the team member who fired it in order for the enemy to take extra damage.

The only 3 damage sources in-game that Mercy cannot boost are:

• Symmetra's Sentries
• Torbjorn's Turret
• Junkrat's Rip Tire

All other ults, including projectiles like Hanzo's Dragonstrike, or D'Va's Self-Destruct can be boosted otherwise.