Unlike other gun damage boosts, Reaper does not affect a gun's splash damage unless the splash does not count as grenade damage (this can be determined on Krieg by seeing which guns can activate Blood Overdrive, but not Blood Bath). Splash damage boosted by Reaper includes:
Also unlike other gun damage boosts, Reaper affects the amp damage of amplify shields.
Reaper affects all enemies who have more than 50% health remaining. This includes enemies with full health but depleted shields. As a result, shielded enemies will take the increased damage until their shields are fully depleted and their health is half depleted.