Snap 2D characters the ground

A characters in a 2D game normally moves freely within a NavMesh / collision boundary. This script causes them to instead snap vertically to the top edge of a collider. If that collider's shape is that of the ground, they will appear to move along the ground without moving vertically inappropriately.

To use it:

1. Create a new GameObject and attach a 2D Collider (e.g. Polygon Collider 2D) to it, and reshape it to match the ground's shape and position.
2. Create a new C# script named StickToGroundY.cs and attach it to your character
3. Configure the Stick To Ground Y's Inspector, assigning its Ground Layer field to match that of the ground GameObject created in step 1.
4. Set the character's starting position to be above the ground, at a distance no more than the length of the component's "Raycast Distance" field.

StickToGroundY.cs:

using UnityEngine;

public class StickToGroundY : MonoBehaviour
{

	public LayerMask groundLayer;
	public float raycastDistance = 1f;
	private RaycastHit2D hitInfo = new RaycastHit2D ();

	private void LateUpdate ()
	{
		hitInfo = Physics2D.Raycast (transform.position + Vector3.up * 0.1f, -Vector3.up, raycastDistance, groundLayer);
		if (hitInfo.collider)
		{
			transform.position = hitInfo.point;
		}
	}

}