Can anyone tell me what the Warlock ability "Chain of Elements" is for?

As someone correctly pointed out, this isn't relevant here; use search next time.

The "Chain of Elements" ability allows you to see which element (water, air, earth, fire) a creature belongs to. When you attack such a creature with a spell of the opposite sign (water-fire, air-earth), additional damage is dealt. By building a structure in your Castle that enhances this ability, you gain the ability to see the elements of your creatures and deal extra damage when they attack. After one hit, the creature's element changes to a random one.
/topic/401/ here is the link, post number 11.