I was sitting here thinking about my two Elvira machines and how I was going to find the third when I had a thought. I wondered how many pinball machines are part of a trilogy. Let's list them here and maybe make some friends. I'll start with the two of the three I have.
Elvira and the party monsters *
Scared Stiff (owned)
Elvira's House of Horrors (owned)
(* Is the missing one)
So let's hear it pinside, what trilogies are out there and what do you own or have played? What did ya think of them?

Ok, what are the other two machines and do you own any of them?

Thank you. This is what I'm talking about. I think it counts as a trilogy even if all the machines are not from the same company. What do you think about that?
May I inquire wish ones you own?

I don't know, what's your reasoning for them being all related in the terminator universe?

Super nice set up but I'll let the forum decide. Nice reach for the extra credit!

What are the 3 rollercoaster machines?

This is one I'm not sure about. I think all four machines you mentioned belong together but the Elvira themed machines definitely belong together. Crossover trilogy perhaps?

Now that is awesome! I didn't know any pinball machines, much less three of them, having ZZ Top music. Well played sir.