4 hours ago, Soakman said:Huh. I guess my assumption is just an assumption maybe then. I would have though that to upgrade from a card, it would need to be present at the start of upgrading a deck. I guess the efficiency of losing an xp if you don't have it in your deck already has usually prevented me from even being in this situation though (when it comes to arcane research).
Looking at how it is worded in the Rules Reference, my inference is that there is a sequence you go through individually for each card (look at the fourth bullet point, where it talks about buying new cards individually). Once you've finished the remove old card/pay XP/add card to deck/check deck size steps for card A, you move on to card B, etc. As a result, your first choice could be to add the level 0 Strange Solution, then your second choice could be to upgrade it to Acidic Ichor (for example).