[Antonio144]

Here's the code for target_z, ie object Y rotation

pawn Code:

// x,y,z arrow position; ax,ay,az, target position
stock Float:GetYRotation(Float:x,Float:y,Float:z, Float:ax, Float:ay, Float:az)
{
    new Float:Yoff;
    new Float:xd = ax - x;
    new Float:yd = ay - y;
    new Float:zd = az - z;
    new Float:dist = floatsqroot(xd*xd+yd*yd+zd*zd);
    Yoff = acos((az-z)/dist);
    return Yoff-180;
}

EDIT: This is 20% faster since it uses two less calculations

pawn Code:

stock Float:GetYRotation(Float:x,Float:y,Float:z, Float:ax, Float:ay, Float:az)
{
    new Float:xd = ax - x;
    new Float:yd = ay - y;
    new Float:dist = floatsqroot(xd*xd+yd*yd);
    new Float:Yoff = atan((z-az)/dist);
    return Yoff-90;
}