In any case, there's an even aron in the lowest level of the undeground train net, that you unlock at some point of the game that I don't remember right now. Basically an aron falls from an iron bar and you can fight it and catch it. I think.
^^^ When you're solving the rail puzzle (when escaping out of the city), you can open two entrances. One leads to outside, the other to a sticker event and lots of stairs, where you can use headbutt (multiple times) on a steel beam to possibly encounter an Aron.
