I've only just started a couple of days ago and still building a deck so I don't have all that much to add to what has probably already been written. I do quite like the Northern Realms faction though, the abilities of the cards are better suited to my play style than the other factions, though I am considering Nilfgaard or Skillege next.
One thing I just discovered and got randomly excited about is how much one Adrenaline Rush card can save one's butt. As the main strength of the Northern Realms is buffs (from what I have seen so far), I managed to buff a Ballista up to 20, copy it using Foltest's ability and apply Resilience to one of them. This was at the end of round 2 against someone playing Monster faction (my natural nemesis >.>) who still had Eredin up their sleeve + an unknown last card due to last draw. If not for Adrenaline Rush I would have lost the battle but with a 20 Str Ballista I just about beat all the points my opponent could muster for the last round. Combining this with Promote could produce fantastic results!
My thought, essentially, was that using Adrenaline Rush can be extremely useful against any faction, and using it against Monsters just feels like a small sweet victory. 'Oh, you get to keep a random card on the battlefield after a round? So can I, but I can choose mine
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