Fan CastingBatman V Superman: Gods Among Us - Part I

Description of Martha Wayne (The Flashpoint Joker/Hallucination):

At another point in the film, Bruce is training himself some more by practicing the art of throwing knives, in the event he may use them against an enemy or two. But as he throws another one of the knives at the target board, he briefly sees the reflection of his mother, Martha Wayne, as the Flashpoint Joker, on the knife. This makes him lose focus and throw the knife into the ground rather than the target board, and afterwards, he curses himself for the loss of focus in that split second, but more importantly, the fact his mother's alternate self still haunts him to this day, more than her actual demise...