Quoted from Hypercoaster:
So that suggests that the only Mechagodzilla footage comes from Terror of Mechagodzilla and not Godzilla vs Mechagodzilla. I'll have to watch those two very closely, but i thought "electromagnetic godzilla" clip was from G v MG not Terror of Mechagodzilla. However, it explains why poor King Caesar don't have his rightful place as a Godzilla ally option. He always gets the shaft, poor King Caesar.
Sterns email is incorrect. The magnet power Godzilla uses was from G vs MG and King Caesar has a lane switch on the playfield. I think they meant to say that Terror of MG was not included.
Edit: just popped on Terror and forgot that key moments from the ending of G vs MG were shown in the beginning of Terror of MG.
So yes, they could easily just be using footage from Terror. Plus I forgot that Titanosaurus is one of the battles so it has to be Terror.