Reforge Discussion, etc.

This hasn't come up yet in story, but yeah, it's possible for a person to be born with the ability to cast in more than one element. It's uncommon but not mind-blowing or anything.

In general, increasing numbers of elemental affiliations are exponentially rarer in the human population. There are some creatures or plants or whatever that are inherently multi-elemental, however.

Spirits can also be composed of more than one element, but that means something a little different than an organism using multiple elements.