TargetDamage.cs

using UnityEngine;
using System.Collections;

public class TargetDamage : MonoBehaviour 
{

	private GameControl control;				//  Access to the GameControl script
	private float damageImpactSpeedSqr;			//	The square value of Damage Impact Speed, for efficient calculation
	private SpriteRenderer spriteRenderer;		//	The reference to this GameObject's sprite renderer

	public Sprite damagedSprite;				//	The reference to our "damaged" sprite

	public int currentHitPoints;				//	The current amount of health our target has taken
	public float damageImpactSpeed;				//	The speed threshold of colliding objects before the target takes damage
	public int hitPoints = 2;					//	The amount of damage our target can take
	
	void Start () {
		spriteRenderer = GetComponent <SpriteRenderer> ();
        control = FindObjectOfType<GameControl>();
        currentHitPoints = hitPoints;

		//	Calculate the Damage Impact Speed Squared from the Damage Impact Speed
		damageImpactSpeedSqr = damageImpactSpeed * damageImpactSpeed;
	}
	
	void OnCollisionEnter2D (Collision2D collision) {
		//	Check the colliding object's tag, and if it is not "Damager", exit this function
		if (collision.collider.tag != "Damager")
			return;

		//	and if it is less than the threshold velocity, exit this function
		if (collision.relativeVelocity.sqrMagnitude < damageImpactSpeedSqr)
			return;

        if (spriteRenderer)
        {
            spriteRenderer.sprite = damagedSprite;
            currentHitPoints--;

            //	If the Current Health is less than or equal to zero, call the Kill() function
            if (currentHitPoints <= 0)
                Kill();
        }

	}
	
	void Kill () {
		//	As the particle system is attached to this GameObject, when Killed, switch off all of the visible behaviours...
		spriteRenderer.enabled = false;
        control.CurrLevel.Currentscore += 8000;
		GetComponent<Collider2D>().enabled = false;
		GetComponent<Rigidbody2D>().isKinematic = true;
        Destroy(this.gameObject,.5f);
		//	... and Play the particle system
		GetComponent<ParticleSystem>().Play();
	}
}