Poltergeist's balancing seems really weird to me. On the one hand, if you bring investigators who fight with Spells or Relics regularly, like Agnes Baker or Sister Mary, these things basically serve as Ghoul Minions with 1 extra fight, barely a roadbump on the way to victory. On the other hand, if you don't bring those investigators, these things can form a significant time suck, requiring you to Parley with them, chanting "Go away, go away, go very much away" until they're gone. And if you didn't bring those investigators and the investigators you did bring have some non-traditional way of gathering clues, like Lockpicks, Drawn to the Flame, or Grete Wagner, meaning that you can usually afford to go without high base , these things become a nightmare, a slog almost like the infamous Base of the Hill from Where Doom Awaits. On the bright side, the Geists can be evaded, but even that's a bit of a tall order at 4 evade, especially since you might have to do so multiple times if you have to double back to where you left it later in the scenario.
The worst part, to me, about these three different difficulty levels ("easy" if you pack Spells or Relics, "somewhat troublesome" if you don't but pack high investigators, "evade because that's virtually the only way you can interact with these things" if neither is true) is how much it feels they penalize players with a limited collection. Yes, it is possible to tech around Poltergeist if you have the full card pool, but, as the Spartan's legendarily said, "If." If you're a new player who's heard good things about Carcosa, bought it, and is facing it with just the Core, good luck. On the other hand, if you're a veteran with a full collection you have so many options for dealing with this things that it basically isn't a challenge anymore. It's not fun when you're starting out because your options are too limited and it's not fun when you're settled in the game because, without its invulnerability, the Poltergeist is incredibly basic.
I believe I understand what FFG was trying to do with the Poltergeist; prevent s from mindlessly going "I attack the enemy" every time they draw an enemy, while also allowing s to provide at least a bit of support in combat. But the way they executed those ideas in Poltergeist just makes me scratch my head and wonder if Striking Fear would be a good replacement set for The Pallid Mask, as it would be more interactive with my current card pool.