I am currently in Electro Valley, with 3356 trophies (having lost 2 battles, the first of which being one that I started when I was at 3,600), which is above the demotion threshold (3,550) for Electro, but above the official number of trophies for Electro, aka the promotion threshold. I am wondering if the cards from Electro (Magic Archer and Zappies) will still show up in the shop. The following quote leads me to believe this may not be the case, but it is not entirely clear. It's been a few months/weeks since my two lost battles (both to cancerous decks, fyi), and I have not seen MA in the shop since then, and I do not remember seeing Zappies in the shop, either.
"Note however, that the Free Chest, Crown Chest, and Shop will all reflect Cards and Gold according to the Arena you are actually qualified for. This is the main difference of being on one side or the other of the threshold." -Ebongo, from his answer to the question at this link: When will you be demoted?
If anyone can help me out, thank you! I'm still probably going to try to push above the official promotion threshold to make my trophy count/arena comparison cleaner, though.