RandomSprite.cs

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

namespace ProD
{
    public class RandomSprite : MonoBehaviour
    {
        public List<Sprite> sprites; /* List of sprites to choose from */
        public float[] weights; /* List of 'weight' values to match against sprites. !!!MUST BE SAME SIZE AS SPRITE LIST!!! */

        void Start() /* Init */
        {
            GetComponent<SpriteRenderer>().sprite = RandomUtility.pickWeighted( sprites, weights ); /* Get a sprite from the list using weight values */
        }
    }
}