Vile Acceleration is a Corrupted Mod for rifles and Bows that increases their fire rate by 15% per rank to 90% at rank 5 but decreases damage by -2.5% per rank to -15% at rank 5. The increase in fire rate is doubled for bows.
The damage reduction is additive. For example, a weapon equipped with maxed Serration and Vile Acceleration would deal 250% of its base damage.
Compared to only a maxed rank Serration, adding a Vile Acceleration represents a loss of only 5.6% damage.
With a max ranked Serration (but without Heavy Caliber), this represents a DPS upgrade over Speed Trigger of about 12% on fully automatic weapons that can take full advantage of the fire rate increase. It does still lead to greater ammo consumption and more frequent reloads though, so keep that in mind when modding your weapon.