Useful Unity (Game Engine) Transform Extensions, LookAt2D (Make the 2D object look at specified position), ...

TransformExtensions.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

/// <summary>
/// Transform extensions.
/// Useful transform utilities and methods.
/// </summary>
public static class TransformExtensions
{

  /// <summary>
  /// Rotates the transform so the forward vector points at target's current position.
  /// </summary>
  /// <param name="transform">Transform.</param>
  /// <param name="target">Target.</param>
  public static void LookAt2D ( this Transform transform, Transform target )
  {
    transform.LookAt2D ( ( Vector2 )target.position );
  }

  /// <summary>
  /// Rotates the transform so the forward vector points at worldPosition.
  /// </summary>
  /// <param name="transform">Transform.</param>
  /// <param name="worldPosition">World position.</param>
  public static void LookAt2D ( this Transform transform, Vector3 worldPosition )
  {
    transform.LookAt2D ( ( Vector2 )worldPosition );
  }

  /// <summary>
  /// Rotates the transform so the forward vector points at worldPosition.
  /// </summary>
  /// <param name="transform">Transform.</param>
  /// <param name="worldPosition">World position.</param>
  public static void LookAt2D ( this Transform transform, Vector2 worldPosition )
  {
    Vector2 distance = worldPosition - ( Vector2 )transform.position;
    transform.eulerAngles = new Vector3 ( 
      transform.eulerAngles.x, 
      transform.eulerAngles.y, 
      Mathf.Atan2 ( distance.y, distance.x ) * Mathf.Rad2Deg );
  }

}