As a Player that likes Gaunlet a lot, after some years, it becomes very mechanic.
I have 3 or 4 decks that clear Gaunlent with more than 95% possibility, (some own brews, others taken from here)
(I have my own raking system, the gaunlet star system)
So whats next step in clearing the gaunlet: Do a 150 card deck.
Have tried diferent combinations, but this deck, its above all of them
with a 2* ranking (meaning at least 6 boss kills) In fact this deck has a 48 win 1 loss (against boss gaunlet, defeated by a snowball...)
Regardig this deck, its simple. Rakano creatures <= 3 cost.
So if you need a new gaunlet challenge, try to make a 150 cards deck.