Although the original text of Doubled Vigilance didn’t allow it to be revealed on-guard per the normal game rules, ICE’s NetRep confirmed that the intention was that it could be revealed in this way, which was added as a card ruling in CRF 8. As such, here is the current text for Doubled Vigilance per the Council of Elrond tournament rules:
Normally the resource player can’t take any actions during the site phase prior to facing automatic-attacks, but with an important caveat:Playable on a Shadow-hold (or on a Ruins & Lairs or Border-hold if Doors of Night is in play). If the company chooses to enter the site, its player must make a roll and subtract its company size. If the result is greater than 6, the company may enter the site as normal. Otherwise, the company must face an attack to be resolved before any automatic-attacks: Orcs — 4 strikes at 9 prowess. Discard when the site card is discarded or returned to its location deck. Can be revealed on-guard.
And per the normal rules of combat:2.V.ii.1 The resource player can only take actions during a company’s site phase after that company has successfully entered its site (but may still take actions during combat prior to entering the site, per the normal rules for combat).
The bolded text above means that whether an attack is taking place during the movement/hazard phase, in the middle of the resolution a chain of effects (when actions can’t normally be taken), or - in this case - prior to facing automatic-attacks during a site phase, the resource player can always take resource/character actions in Step 1 of combat that would either cancel the attack or modify attributes of the attack as a whole. Specifically against an attack from a Doubled Vigilance revealed on-guard (or against a Siege attack, as another example), the resource player could play Escape to cancel the attack, or tap a Black Arrow to give -1 to the attack’s prowess, etc.3.i Combat, Step 1 (Pre-Assignment Actions) - Prior to strikes being assigned, either player may take actions that they would normally be allowed to take during the current phase of the game in which combat is taking place (e.g. during a site phase, only the actions prescribed below may be taken prior to entering a site; during a movement/hazard phase, the company’s hazard limit is still in effect, etc.). Regardless of the phase of the game in which combat is taking place, the resource player may take resource/character actions, and the hazard player may take hazard actions if combat is taking place during a movement/hazard phase, that would either:Players cannot take actions that cancel the attack or modify the attack as a whole after this step, which continues until both players have finished taking actions prior to strike assignment.
- cancel the attack
- modify attributes of the attack as a whole (e.g. the number of strikes, which player assigns strikes, the prowess or body of the attack, etc.).
Furthermore, the resource player is always allowed to take specified resource/character actions during a Strike Sequence, again regardless of when the attack is taking place:
Any of these resource/character actions may therefore also be done during combat resulting from a Doubled Vigilance that is revealed on-guard, including playing resources like Lucky Strike, Dodge, etc.3.iv.3 Strike Sequence, Step 3 (Applying -3 to Stay Untapped) - A defending resource player may apply a temporary -3 modification to the prowess of the character facing the strike in order to prevent the character from tapping after the strike.
3.iv.4 Strike Sequence, Step 4 (Tapping for +1 Support) - A defending resource player may tap one or more of their untapped characters in the same company who hasn’t been assigned a strike (even if the character wasn’t allowed to face the attack) to “support” by applying a temporary +1 modification to the prowess of the character facing the strike.
3.iv.5 Strike Sequence, Step 5 (Defending Player Actions) - A defending resource player may play resources, and/or may take resource/character actions on the character facing the strike and the non-follower cards it controls, if doing so would affect the resolution of the strike. This does not include actions that would tap the character facing the strike but that wouldn’t otherwise affect the strike. Only one resource that requires a skill may be played during this step (but multiple resources that require skill may be played outside of this step).
With all of that said, only the aforementioned actions are explicitly allowed in combat regardless of when it is taking place, so other actions cannot be taken if the attack occurs during the resolution of a chain of effects or - in this case - prior to having faced automatic-attacks during a site phase. And so it is worth noting, per the CoE rules:
This means that while you could normally use Marvels Told/Voices of Malice to stop an attack from an in-play hazard’s passive condition prior to its attack resolving into combat (e.g. from an Ahunt Dragon), there is no opportunity to play them against a Doubled Vigilance revealed on-guard because the earliest time to play them would be during Step 1 of combat but, per Rule 3.1.2, they would not be able to cancel the attack at that point and thus would not be allowed. So if your company loses the dice roll of an on-guard Doubled Vigilance, they do have to face the Orc attack - but at least you can take the specified resource/character actions to help them get through it!3.1.2 Once an attack resolves into combat in a chain of effects, it can no longer be canceled by the card that created the attack leaving play.