|First appearance||Trilby's Notes|
|Kindred||Jacob O'Malley (ancestor)|
Siobhan O'Malley is a character in Ben Yahtzee Croshaw's game Trilby's Notes.
She later invites Trilby to her own room to answer questions involving her family history. Once there, she begins asking questions about the DeFoe Manor Incident and brings up the topic of Trilby the cat burglar, who was rumored to have been involved in the event. Via his dated clothing and transparent disguise, she uncovers Trilby as the one and only. The discovery shocks the gentleman enough to turn his mood against him and warp him back to the alternate hotel where he is faced by the Tall Man. Just as the Tall Man closes in on him he manages to fight back with a strong kick aimed at the demon's featureless face, only to be phased back, instead knocking out Siobhan.
When she awakes a short time later the memory of the little mishap floods back, filling her with enough negativity to phase her into the alternate hotel.
Later, she finds Trilby on the roof of the hotel and inquires him about the bizarre and haunting realm they've been sent to. Trilby reminds of a previous warning he had given her about the dark and unappealing path he leads before presenting her with his tranquilizer pills, claiming to no longer need them.
At the climax of the game, she finds Trilby just in time to witness his final encounter with Lenkmann, before the man sends a knife through Trilby's torso. Bound and gagged, she can do nothing while Lenkmann performs a summoning ritual around Trilby's weak and immobilized form. She watches as the bleeding man dies, moments before Cabadath can reach him. Displeased with the dead burglar, the demon turns on Lenkmann, and the two disappear, leaving Siobhan to attempt CPR on Trilby's lifeless body. He revives, to her relief, though unknowingly not by her hand.
- Siobhan is described by Abed as "drinking too much for her age" and it is implied that her and Abed had some form of "relationship". This is backed by Yahtzee's commentary in the special edition.
- Also according to the commentary, she was meant to make sexual advances on Trilby after luring him with information on her family history.