I tend to consider mainlines any casting that came in a standard HW package. Hi-Rakers came in a standard pack, with just a bit more writing on them. I would say extras are mainline also. Scene Machines had their own packaging so I'd say no. However, some things change over time. For example, Real Riders used to be mainline, but are now special editions or limited series. That said, a TH with real riders would be considered mainline.