When the players collectively perform the Ritual of Terror, whose Action is it?
Rituals that are not explicitly associated with one Spirit are Spirit Actions for the purpose of anything that cares what type of Action they are (e.g., Vengeance as a Burning Plague destroying its Presence as part of a Ritual of Terror), but are not an individual Spirit's Action for the purpose of their Special Rules. (No, not even in solo play, for the sake of consistency.)