Well, what happened was:
Mary was the demon's slave, and apparently so was Tira. There are only two ways to get out of being baba yaga's slave, and those are to either: Kill yourself, or to trick someone into doing something evil--as explained by the movie.
Mary did indeed take the kids to feed the demon. And then she killed herself to be free of it (possibly from guilt after being accused of it).
Tira (the model holding the baby) on the other hand, tricked Jess by lying to her that baba yaga is just an internet fairy tale, and that to save her daughter, she had to find the real kidnapper. This made Jess believe that the detective was the kidnapper, and through a series of events, Jess led the detective to the demon, effectively fulfilling the part where she was "tricked into doing something evil". At the end, Tira killed the husband to get rid of the evidence that she herself probably planted (the folder containing the interrogation with the detective), and her mark disappeared, because she was now freed of the demon's enslavement. The ending scene, was Jess being branded with the seal of the demon, concluding that she is now officially the demon's new slave.
Mary was the demon's slave, and apparently so was Tira. There are only two ways to get out of being baba yaga's slave, and those are to either: Kill yourself, or to trick someone into doing something evil--as explained by the movie.
Mary did indeed take the kids to feed the demon. And then she killed herself to be free of it (possibly from guilt after being accused of it).
Tira (the model holding the baby) on the other hand, tricked Jess by lying to her that baba yaga is just an internet fairy tale, and that to save her daughter, she had to find the real kidnapper. This made Jess believe that the detective was the kidnapper, and through a series of events, Jess led the detective to the demon, effectively fulfilling the part where she was "tricked into doing something evil". At the end, Tira killed the husband to get rid of the evidence that she herself probably planted (the folder containing the interrogation with the detective), and her mark disappeared, because she was now freed of the demon's enslavement. The ending scene, was Jess being branded with the seal of the demon, concluding that she is now officially the demon's new slave.