Mirroring
The entity at the end of the film mirrors Lena's movements exactly as she does them. This leads eventually to Lena placing a phosphorus grenade in the entity's hand which eventually kills it and stops "The Shimmer". This imagery relates to how Lena is able to kill the self-destructive part of herself that is attempting to take over, unlike everyone else who has been overcome by it.
Lena and Kane
Kane hugs Lena at the end of the film even though she knows he isn't her husband. The imagery her in the midst of the sci-fi thriller relates to the realities of war, as many soldiers come home from the battlefield changes in ways that are profound, many don't recognize who they are from when they started. Thus, this scene is a representation to those who've faced war and lived.
Down the Hole
Lena is seen going down the hole into the center of the creation of "The Shimmer" where Ventress is, just beneath the lighthouse. Lena is surrounded by darkness except by the black of the hole. This image shows us that she's been cornered into going directly to the source of the darkness in order to find answers, she isn't able to stay in the light any longer.
Josie
Josie walks away from Lena, deciding not to fight "The Shimmer" any longer. She, instead, becomes part of it, as she becomes a flower person. The imagery reveals that she becomes what she is most intent on: surrender to the inevitable. Thus, as a flower she is a part of the ecosystem, but not a threat to its destruction nor in need of it to evolve.
