Basically, when the enemy takes damage, the ID of the element changes to the one it's weakest to just for the resistance calculation step. That means if you're hitting a skeleton with fire, it will be effective damage. However, if it "Greatly Resists Ice", then your damage will be lowered from that effect.
I don't have a list handy, but I can say that most explosion effects will have it's range increased from this. I'll make a note to check this again and come back with a list eventually of all the spells that should support this.
Once you reach Mythic League and pass 1000 points, you'll at least be able to see what your overall standing is