I remember years ago it might have had something to do with skitters? I don't want the potion though. Thanks for any advise.

Zombieness is available all year round if you have unlocked zombie skins in your wardrobe.

With the changes last year to Survival (Valentine's) you are able to unlock new (and older) skins every february - so if you don't have any you will have to wait ~3 more months :)

I will go look at my skins, thanks.