So guys i started make a game, a fighting game with Soul shatters mechanics (meele combat), and Elemental Battlegrounds (Elements + you can make your own skill set), but i wanted something new, so, i started make elemental interactions, for example: Imagine you use a Rock Skill, than a person use a fire ball on the Rock, so the rock will start burn, and will do burn damage.
Now imagine i use the same skil on a Ice skill:
I know the effects are poor but iam not effect maker, just scripter … (effects on client), with that system you can do cool things, like a fire tornado, or a ice tornado, if you use a water skill on a allie that is burning it will remove the fire, you can use a water skill to cancel some fire skill for example, or a ice skill to cancel a water skill, etc, etc, its a cool idea 
i hope you guys enjoy the idea.