Quote from Card Slinger J »Reprinting them through The List is only going to make these cards much harder to obtain with whales hoarding so much sealed product containing them not to mention how bad the pull rates are.
Okay, let's say it again.
Every Set Booster Box for New Capenna is expected to have 3-4 "magic-ized" Stranger Things Cards (one per 8 set boosters). That is about the rarity of a normal mythic card. For every 3 copies of *Insert 3-color demon mob boss mythic* New Capenna puts in circulation, I would expect between 1 and 2 copies of a magic-ized Will or Mindflayer to be circulating.
While most mythics will technically be more common (as you won't be able to crack this from a Collector/Draft booster), these cards should be more common than something like Lynde in Midnight hunt due to the GREATLY increased pull rate. These will not be rare in the sense that box toppers or expeditions are.