The lyrium dagger in Dragon Age: The Veilguard has an inordinate amount of influence over the game's narrative, despite having never been mentioned in the series before its appearance in the prologue of The Veilguard. However, this may not be the case. The dagger in question could have been foreshadowed in Dragon Age: Inquisition, after all.
This was spotted by the observant NovaShyne on Reddit who happened across snippets of dialogue with Solas on a replay of Dragon Age: Inquisition. It should be noted that Solas does use the word dagger in other contexts in Inquisition, so not every example of him mentioning a dagger is necessarily a reference to the lyrium dagger.
All of this dialogue takes place in the conversation between the Inquisitor and Solas about blood magic. The first mention of a dagger occurs when Solas says "I once saw a woman stabbed in the stomach with a dagger. She died slowly, in agony. It was repulsive." As the poster points out, we know that Mythal was murdered with the lyrium dagger, so this could be a reference to that event. However, Solas referring to Mythal as just "a woman" is unlikely given their relationship.
The Inquisitor...
