currently there's no visual cue on-buy that either swamp hag or haunted woods is in play; that would be nice!
More generally, I expect to eventually see my / other players durations in play and reserve mat, native village mat etc.
MF's implementation of this was actually pretty good (changing the color of the gain button). That would probably work here, but maybe not quite so well since you can just click on the actual card to buy it. Maybe a differently colored border around the cards you can buy?