Also, the next Adventure Game featuring the Cybermen feature the return of Cybermats, which have only ever been seen with the original Cybermen.

Yes indeed.

Yeah but, the Cybusmen were brains in shells. It doesn't matter what the Mondas Cybermen were, the Cybusmen were not the Mondas Cybermen. It just glares of poor continuity for a cheap shock to me, not to mention it was pretty lame that the thing was trying to eat Amy's head like a cartoon clam.

I think if you see the trailer for the next game, it reveals what it was trying to do. The trailer features humans with only their heads replaced by cyberheads, they're gonna be Cyberslaves, so I think that is what the head attempting with Amy... tbh, that's quite a scary concept, I like it.

that doesn't explain the arm though

Sure it does. Cybermen can, in an emergency, kick into Cyberslave mode. That was its only option at the time so it pursued it.

I guess that makes sense.

ergo, scary