Can you activate Reaction cards and hidden cards on your turn with an empty stack, or do Reactions only respond to other cards?

Ruling: You can play Reaction cards to start a chain on your turn when you have priority, even with an empty stack. Reactions function as regular actions but can also be used in response to other cards.

Nuances:

• Hidden cards can be played anytime you have priority, as long as at least one turn has passed since you hid the card
• Each ability speed can be used at any of the speeds "above" it (Reactions can be played at Action or Base speed, Actions can be played at Base speed)