Can unit abilities (like Miss Fortune's ability that activates when she moves) be countered with cards like Defy, and do they open a chain?

Ruling: Unit abilities do open a chain, but they are not spells and therefore cannot be countered by current counter cards like Defy or Wind Wall, which specifically counter spells not abilities.

Nuances:

• The distinction between spells and abilities is critical for determining what can counter them
• Current counter cards in the game (Defy, Wind Wall) only work on spells