i got some items

[Super]

They are called 'Interactive Sets' but that can mean any motorized train set. What piqued my ears was your mention of "my theory is that the small back square is for it to interact with interactive sets" which led me to think there was some action that the engines perform, possibly with scenery pieces. I do know of the Billboard that works when a train passes underneath but thats just a momentary button that the wheels roll over to activate. I recall another action accessory for the Underground Erinie but that could just mean my grey cells are fading