Are gasmasks allowed in classic?
 

Bruh

As hats? There were a few a long time ago.

As shields/on heads? No, it would be denied for acting as a substitute for a hat.

So they're allowed, or there's a specific rules for it?

Yes, as hats (and maybe accessories, now that I think of it). I don't believe there are any rules specific to gas masks.

This question is kind of off-topic, are accessories like shoulderpads in hat allowed?

Graphics staff might know better than I would, but I would guess that in the future shoulder pads are probably going to be sold as accessories.

I think if you made a sort of helmet with shoulder pads that might be fine as just a hat. Then again, it may be better to separate it into two items if you were planning on submitting something like that for Christmas. Not 100% certain as I am not a part of the graphics team.