Escape the Dark Castle: Adventure Pack 2 – Scourge of the Undead Queen

From BoardGameGeek:

This Adventure Pack introduces a new mechanic to the system - Companions. These characters can appear during a quest and join-up with the prisoners to assist in their escape. Fans of roleplaying games will know them by the term NPCs (non-player characters). Players will now encounter event cards in the item deck which trigger the arrival of one of the Companions. Each Companion has a unique mixture of traits and a special ability. They are powerful allies but their presence may be fleeting, so prisoners must choose carefully how and when to call on them.