Your confusion, I believe stems from the fact that you can only have 1 card of each character to buy from. You need to pick to use either the lesser or the greater.
The Lesser allows you to buy any 'fiend' dice ( pit fiend and other with fiend in the name) for 2 less than the normal cost.
The Greater allows you to field any fiend dice (if you have/draw more than 1 for your roll) for 2 less energy.
There is no confusion. And you missed to explain if it is only "this" one turn that the text works or over more text like a "while active" . The only thing i cannot believe is, that you need so much luck to have fiends in one draw that it makes the card, except the paragon one, useless.