NB: ArkhamDB now incorporates errata from the Arkham Horror FAQ in its card text, so the ArkhamDB text and the card image above differ, as the ArkhamDB text has been edited to contain this erratum (updated August 2022): Erratum: The Lunatic trait in this card's effects should read Possessed wherever it appears, instead. - FAQ, v.2.0, August 2022
Treachery cards do not have a header for their subtitle. If the title of a treachery card contains 1 or more words in parentheses, that is considered to be its subtitle. Other cards with the same title and a different subtitle are still considered to be copies of one another. e.g. Restless Journey (Fallacy) and Restless Journey (Hardship) are both copies of Restless Journey. - FAQ, v.2.0, Card Ability Interpretation 2.21, see Treachery Subtitles.
Revelation - Secretly add Gift of Madness (Pity) to your hand.
You cannot attack Lunatic enemies.
: Randomly choose 1 enemy from among the set-aside Monster enemies and place it beneath the act deck without looking at it. Discard Gift of Madness (Pity) from your hand.
Q: When no more set-aside Monster enemies left, can I trigger action ability on this card to discard?
RR "Target" says :
The term "choose" indicates that one or more targets must be chosen in order for an ability to resolve. The player resolving the ability must choose a game element (usually a card) that meets the targeting requirements of the ability.
If an ability requires the choosing of a target, and there is no valid target (or not enough valid targets), the ability cannot be initiated.