There's two things: the damage boost upon deployment (aka small damage boost) and the regular boost the VM gives when attacking a building.
Small damage boost: equal to half of the VM's normal damage boost. Any nearby unit when the VM is first deployed will gain this small boost and it will last for the entire raid (or until that troop(s) being affected dies).
Normal damage boost: when the VM is attacking a buildinrgg, he does damage and makes that targeted building take more damage until it is destroyed. Will only affect one building at a time, but he does small splash damage so it is possible it could affect multiple defending CC units at a time.
Get it now?
