Answer: EATEN
First, notice that all these Dominion cards are +cards, +actions, +buys, and/or +$, and nothing else. Also, “elfin snot rot marinara” is an anagram of “linear transformation”. In fact, the bizarre transformation Hermione is talking about is a linear automorphism on the four-dimensional vector space spanned by the basis vectors {card, action, buy, $}! Since this order of the basis vectors is canonical, you can represent this linear transformation with a matrix, whose entries are all numbers between 1 and 26.
These spell out THE ANSWER IS EATEN.