The element die has sides for Earth, Air, Fire and Water. It is primarily designed for roleplaying or storytelling games, where it can be used to figure out the kinds of magic an enemy might have, or what their weaknesses are.
Like the regular d4, the roll is shown by the symbol at pointing up when the die is rolled. This will be the same on all three sides showing.
This die was added to the system since the cards shown on the cards page were rendered, so doesn't appear on those cards.