De acordo com Will no episódio da temporada 3, O teste da sauna, parece que a maior parte do Mind Flayer ainda pode existir no Upside Down e provavelmente está executando o programa a partir daí, outra parte ainda existia em Hawkins, pois ele (ou pelo menos essa parte) estava tentando se tornar mais corporal durante a temporada 3.
3.04 Transcript:
WILL: I didn't think it was anything at first. I mean, I think I just
didn't want to believe it. The first time I felt it was at Day of the
Dead.
MIKE: Power went out that night, too.-
WILL: And then I felt it again at the field near the Nelson farm the
next day. Then again yesterday outside Castle Byers.
MAX: What does it feel like?
WILL: It's almost like You know when you drop on a roller coaster? -
MIKE: Sure.
MAX: Yeah.
ELEVEN: No.
WILL: It's like everything inside your body is just sinking all at
once, but this is worse. Your body it goes cold and and you can't
breathe. I've felt it before, whenever he was close.
MAX: Whenever who was close?
WILL: The Mind Flayer.
Eleven: I closed the gate.
WILL: I know, but what if he never left? What if we locked him out
here with us? This is him. All of him. But, that day on the field, a
part of him attached itself to me. My mom got it out of me and Eleven
closed the gate. But the part that was still in me, what if it's still
in our world? In Hawkins.
MAX: I don't understand.The Demodogs died when El closed the gate. If
the brain dies, the body dies.
WILL: We can't take any chances. We need to assume the worst. The Mind
Flayer's back. Yeah. And if he is, he'd want to attach himself to
someone again. A new me.
LUCAS: A new host.
ELEVEN: How can you tell if someone is a host?
Além disso, há até uma breve conversa das crianças em outra cena sobre "misturar produtos químicos" para criar "uma nova substância" para explicar por que as vítimas estavam comendo certas coisas, mas com toda a honestidade, não há informações suficientes para entender necessariamente o plano completo de Mind Flayer com a subparcela que consome produtos químicos.