how do i make a SWEP shoot an ent Down usingSetVelocity()?

im trying to spawn an Ent up in the air (got that part sorted)and make it shoot Directly down using SetVelocity(Vector(0,0,0)). what values would I need to add in place of the 0s?

Thanks.

Vector(0,0,-speed)

Yeah, I got it once I figured out you need a speed for velocity. lol