HealthLogic.cs

using UnityEngine;
using System.Collections;

public class HealthLogic : MonoBehaviour {

    // Debugging
    public bool loggingEnabled = false;

    // Stats
    public float health = 10;
    public float maxHealth = 10;
    public float invulnerabilityPeriod = 0.2f;
    [Range(0.0f,1.0f)] public float invulnOpacity = 0.5f;

    // Other
    public bool playsSoundOnHit = false;

    private float oldOpacity;
    private float invulnTime = 0;

    // Initialization
    void Start ()
    {
        oldOpacity = this.renderer.material.color.a;
    }

    void LateUpdate ()
    {
        if (loggingEnabled)
            Debug.Log (health);
    }

    public bool Damage (float amount)
    {
        if (Time.time > invulnTime)
        {
            health -= amount;
            invulnTime = Time.time + invulnerabilityPeriod;

            if (playsSoundOnHit)
                audio.Play ();

            if (health <= 0)
            {
                if (this.tag == "Player")
                    Application.LoadLevel (0);
                else
                    Destroy (gameObject);
            }
            else
            {
                Color color = this.renderer.material.color;
                color.a = invulnOpacity;
                this.renderer.material.color = color;

                StartCoroutine (normalizeOpacity (invulnerabilityPeriod));
            }
        }
        return false;
    }

    private IEnumerator normalizeOpacity (float delay)
    {
        yield return new WaitForSeconds (delay);

        Color color = this.renderer.material.color;
        color.a = oldOpacity;
        this.renderer.material.color = color;
    }
}