Hi, you can spawn your enemies on top then give them the bullet behavior with an angle of motion of 90 to move down.
Then, to satisfy your "come closer" request, you add a condition that once the enemy has traveled X amount such as 200 then set his speed to zero.
That way enemies will spawn on top, move down for 200 and stop.
TIP: use invisible sprites to move stuff and PIN the graphics on top. That way you don't have to worry about angles and bad collisions.