The Elements of the Magical World:
Fire: The element of passion and rage, destructive in it's nature.
Weakness: Water and Earth
Strength: Nature/Plant Metal, and Ice.
Water: The element that fills the oceans, adaptable and ever moving.
Weakness: Electricity/Lightning, Wind, and Ice.
Strength: Fire and Earth
Earth: The solid element, strong and immovable.
Weakness: Water and Nature/Plant
Strength: Fire, Lightning/Electricity, and Air/Wind/Sky
Air/Wind/Sky: The air we breathe, constantly moving.
Weakness: Earth and Metal
Strength: Water
Lightning/Electricity: Bright death from a stormy sky, shocking to the touch.
Weakness: Earth
Strength: Metal and Water
Ice: Frozen, cold, not as free flowing like water, but sturdy like earth.
Weakness: Fire
Strength: Water and Nature/Plant
Metal: Created from the earth, and just as strong, but shinier.
Weakness: Fire and Lightning/Electricity
Strength: Wind
Nature/Plant: The element of life, plants like the grass and trees that fill the earth.
Weakness: Ice and Fire
Strength: Earth
Darkness: The shadow, the dark, where the monsters of the night live.
Weakness: None
Strength: None
(Even with Light)
Light: Bright, illuminating, the counter to darkness.
Weakness: None
Strength: None
(Even with Darkness)
Neutral elements include anything not listed above, meaning they have no strength, and no weakness.
There are some extras like sand, which is weak to fire, rubber which is strong to electricity but weak to sharp metal, etc. Some of these will need mod rulings, or confirmation.