Presumably, an element is just a general term for an area of focus, so anything could be an element. However the only ones used in story were wind, water, wood, fire, earth, air, and metal. There are many kinds of practitioners that work with elements. Elementists can bind elementals to housings to use at a later time. Blood Mages can empower an element's effect either mildly for a "long" time or as a powerful, short burst. Ogre Mages can combine their actions with elements in a "bender" sort of way.
↑Elements - the ____ stuff. Practitioners and practitioner families generally have areas they focus on. One family might dwell on steel, chains, blades, etc. Another might do blades, red hot metal, fire. Another could do glass, crystal, ice. Another might do silence, deafness, echoes. Familiars often contribute to this, either complimentary or something else in the bag of tricks. They generally play off of each other in some way.
Sparks - Produces energy as part of the move or art. Burns foes. Defensive/utility benefit - Following a round where they didn't miss or get hurt, they can attack one additional time.
Lightning - Produces arcs of electricity. Damages machines, may chain to hit an additional foe. Utility/defense: Move faster and evade more easily.
The question bought us a moment’s pursuit. Had the vessels been uniform in size and shape, I imagined it would be a march, a dozen hard feet hitting ground at the same moment. But they weren’t. It was a shuffle.