Penny is inspired by Theren, who speaks to his pateon in his head. She asks inside her own head "Are you there?" and gets an answer. The unknown entity identifies as "The Forgotten One". She tells this to the others, but when asking for another name for the entity, it replies "It is not time yet".
Nezznar Khalazza talked about the Forgotten One
Probably related to the key, and her newfound abilities as a sorceress.
In the Stairs of Aranon, they ask the Monk a question about the "key", and here is what they found
Penny is very hesitant to give away the key to the monk. The voice in her head tells her not to do it. Kal notices that something is amiss. She asks to see the key, but Penny won’t let her hold it. The monk explains that Penny has made a deal with the “Forgotten One”. He is not the best person to give her what she wants. He is not an honest god. The key is the holy symbol of the Forgotten God. They trapped him when he betrayed them and tried to kill them. The monk reassures them that she is not in danger, but to be aware that they should let him go eventually and to keep the key hidden. Someone is probably searching for it.
Penny emphasises that she can trust everybody in the group to not take it from her.
After returning back from their ventures in the North, Penny reveals that she has learned to read. Once asked by Willowbark, she tells them that her patron taught her. She also tells them she can read the ring, and Willow again asks what the ring says. Penny reads the inscription, omiting the name of her patron, afterwards only naming hiom as "The Forgotten One". It has an ominous message about a "person" being killed and ressurrected, becoming the God of Destruction and Decay, forever to be part of the Pantheon