Of all of the elements, the only one that I know has a specific trait associated with it is Holy, who has multiple heroes capable of blinding the enemy (Bane, Joon, Hu Tao, etc).
What are the primary characteristics that separate one element from the other? Is there a pattern that SGG follows when deciding to which element a new hero belongs?
UPDATE TO INCLUDE QUICK ANSWERS BASED ON RESPONSES BELOW:
Holy: Mana control
Dark: Poison damage
Fire: Burn damage
MY CONJECTURE ON THE OTHER TWO:
Ice: Defense buff/Debuff