Back to basic, a magic must have
Ok for alot of people back to basics is a little nightmare pull, all your fancy combos go out the door as your monsters have no abilities. I personally the best way to go for this is magic strong followed by health strong. I am lucky enough to have an Alric so I always go him, if his not around then in going for thorns. The only real counter is that annoying reflecting summoner but it's a rare battle that appears.
Ok so why magic? Well for one alot of people go for higher armoured guys and since all magic reduction and shielding is gone your just hitting straight health! It'd also for the reason my front tank is normally a high health with a little armour.
Second thing you want to do is go all magic on everything but the first one, making sure your highest magic damage guys are at the back to maximise that damage.
Third thing, it's better to fill every slot then get more damage, why you ask? Because a 1 health magic dealer can take a big hit that might have wiped out your one tank, we are aiming to outlast. Also I'm reverse fewer monsters means a big hit might get taken by a chicken, rather then 6 hits that are going to land more efficiently.
So in summary, go magic, fill every slot, go for health
As always use my referral failingforwards when signing up and getting a spellbook and ill send a card