You already got the characters skins right for the season next month.Do the devs plan any kind of event on halloween?maybe a special campaign mission where you fight ghosts,or witches or something.Maybe thr witches can have a attachment card that turns you into a frog and you can't atack for 2 turns,I dunno something
Seasonal quests would be kind of interesting. Maybe some special items only available when the quests are active during that particular season. Nothing overpowering, but something just showing you were around during that time.
I like the idea of seasonal items, but the problem is that nobody else can see them. How about this...an optional "Trinket" slot with seasonal or other cosmetic items. Each would have a small number of cards that can be played during the game which have Cantrip. So, a "Candy Cane" item might have a "Merry Christmas" card that has no effect in-game, but can be played as a message to your opponent, or turns your character model into Santa Claus, or something like that.
It would be kind of hard to balance them as cards, no matter which way it's done. If they were cards with Cantrip, it's still a dead draw. If had Cantrip and it let you draw a new card, it still serves as a substitute for discard effects or hinders opponents cards like Elvish Insight (They'll see that card and then it will immediately get replaced with something new, so they can't see your entire hand.) Even if it was just a Trait with no effect, because of the 3-attachment limit it could push off something else and affect gameplay. Maybe if there was a way to toggle alternate card art on and off? Not just by having alternate holiday themed items, but replacing card art on existing items with holiday versions. For example, if the normal version of Winds Of War could be replaced with one that had christmas trees blowing in the wind instead.
I used to play a CCG on Facebook that used to do the alternative art for events like mentioned. I could see it working here as well - should probably not be that hard even? Just a temporary switch in art files for the period.