“A Goblin launches forward with its knife held tightly between its small hands, it rolls a 15 to hit the Wizard.”, “I cast my Defensive Spell as a Reaction, hoping to stop its attack.”
You can spend 1 Energy to use one of your Prepared Actions during another Creature’s Turn, in response to one of its Actions (you also need to pay that Action’s Energy cost as well, if any). A Reactions takes precedence and resolves first, and can potentially cause the original Creature’s Action to fail.
Reaction cannot be Reacted to. You can use a Reaction only in response to another Creature’s Actions. There is no limit to how many times an Action can be Reacted to. If multiple reactions are taken: the first creature performs its reactions, it resolves, and the GM continues, and describe the outcome of the second reactions, then the third and so on.
(Optional Rule) — Instant Speed:
Reactions can be reacted to.