ok.
there are at max 3 copies of a unique card in a deck.
39 max cards in a deck.
you have a 1/13 chance AT BEST of drawing grandmaster whoever
assuming they did not play ANY cards and that they have 3 copies of a finisher card.
We can refine the math tho.
Assuming you have Mind whatever in your hand on P2T2 (which is too much math for me), and your opponent was smart and only included 2 copies in their deck you actually have a