From Xarthisius to where we are going...
So, again, Xarthisius.
Considering CDPR make him 10 str, I figure CDPR think his ability is somewhat only "moderate", however I don't think this is the case.
Previously, one can only guess opponent's deck base on their played card and leader, and NF reveal, however this card let you see the opponent's whole deck, and in exact order.
Now I know it is still an unpopular card because few bother to remember or record all the cards and their order... HOWEVER, how long will it take for things like gwentup or gwent tracker to totally abuse its ability?
With addon the users can easily watch all the opponent's deck, and know exactly which the opponent is gonna draw, if you played reveal deck, you will know how much this is gonna screw up the game.
(contrary to some other says that information is useless, knowing other's hand and play accordingly is extremely powerful in the last two rounds)
I really don't think such ability should exist in the game, if CDPR want to make Xarthisius viable, simply change it to 5tre and watch the top 3 cards of opponent's deck, and put under whichever you want (can put multiple to the bottom), knowing the full deck is an weapon too OP