[DllImport( "user32.dll" )]
static extern void mouse_event( uint dwFlags, uint dx, uint dy, uint dwData, int dwExtraInfo ); // 마우스 이동
[DllImport( " user32.dll" )]
static extern int SetCursorPos( int x, int y );  // 마우스 클릭

public enum MouseFlags {
            LEFTDOWN = 0x00000002,
            LEFTUP = 0x00000004,
            LEFTCLICK = 0x203,
            MIDDLEDOWN = 0x00000020,
            MIDDLEUP = 0x00000040,
            MOVE = 0x00000001,
            ABSOLUTE = 0x00008000,
            RIGHTDOWN = 0x00000008,
            RIGHTUP = 0x00000010,
            RIGHTCLICK = 0x206,
            MOUSE_WHEEL = 0x00000800
}

SetCursorPos(500, 400);
mouse_event(MouseFlags.MOUSE_WHEEL, 0, 0, -250, 0); // 휠 아래로

mouse_event(MOUSEEVENTF_ABSOLUTE | MOUSEEVENTF_MOVE, X, Y, 0, 0);
mouse_event(MOUSEEVENTF_ABSOLUTE | MOUSEEVENTF_LEFTDOWN | MOUSEEVENTF_LEFTUP, X, Y, 0, 0);