As we know, Past Stages are a huge part of SSF2, and it's very likely that more will be added with the coming versions.

Let's save ourself a little work later on and try to figure out what legal category a past stage might be in if added, assuming it keeps properties such as its size:character ratio identical to the original incarnation and is impacted by the hazard switch.

• This isn't a speculation topic where we post what stages we think are going to be in. We're assuming that anything can potentially be added no matter how off-the-wall. This is just to theorize what impact the hazard switch will have on any that might be added.
• For the purposes of this topic, stages from fan projects such as Project M or Brawl+/- will be counted as past stages.

I could see Port Town Aero Dive working as a counterpick, as well as Brinstar.

I think Magicant and Reset Bomb Forest could work as counterpicks.

I can ALMOST see Peach's Castle 64 working, assuming that the floating slopes are counted as hazards along with the bumper.

Luigi's Mansion sans the pillars I can also easily see.