At least for the first several turns or first half of the game, Master Nguyen’s hero power worked fine and I picked from 2 options like usual each turn. After that, it was stuck on discover a minion for the rest of the game… and was the only option.
I was playing as Sire - and chose whatever the one is that’s +12/12 at the start of each turn.
I have a screenshot, but following the instructions doesn’t seem to work here.