The opponent loses but never has any clear thing to point to
As revealed on the Weekly MTG stream, the cards are: Cecily, Haunted Mage (Eleven, the Mage) Bjorna, Nightfall Alchemist (Lucas, the Sharpshooter) Arvinox, the Mind Flail (Mind Flayer, the Shadow) Wernog, Rider's Chaplain (Will the Wise) Sophina, Spearsage Deserter (Chief Jim Hopper) Othelm, Sigardian Outcast (Mike, the Dungeon Master) Hargilde, Kindly Runechanter (Dustin, Gadget Genius) Elmar, Ulvenwald Informant (Max, the Daredevil) Havengul Laboratory Mystery (Hawkins National Laboratory Upside Down) One very important thing to note is that, unlike the Ikoria: Lair of Behemoth Godzilla cards, or Innistrad: Crimson Vow's Dracula cards, these make absolutely no reference to their Stranger Things origins
And what are the best ways to support them
If an effect copies an Adventure spell, that copy is exiled as it resolves
These are copiable values of the token that other effects may copy