does anyone know how to defeat the final boss? and if anyone has a good deck
I recommend a fairy fire/fairy witch deck. Fairy fire damage will continually climb as the match drags on . Even if the witch's bleeds and fairy fires can't punch through the boss's healing initially it'll just simply be a matter of time before the fairy fire damage gets too big for the boss to heal through. If you got an absurd height advantage on the boss stomp card will do the trick as well. Fairy witch is just an uncommon and you only need 2 at most for a good deck. This honestly makes it one of the most obtainable Valeria killing worthy decks.
What's most important is that fixed damage cards are basically useless against Valeria since their unmodifiable damage is basically too low to be of any use against her huge healing. What you ultimately need are cards that have their damage grow based on a certain condition and then setting things up for the condition to ultimately have the damage grow to absurdity. Unfortunately Ultimate Dark Fairy Queen and A.E.R.A. aren't allowed the damage Valeria so those 2 easy wins won't work.