5, slow : I jokingly call it sandworm wars, they are really good here, also cube and lord A. or similar tanks are much tankier than usual.
6, ranged can do melee attacks: don't put ranged monsters into 1st position, melee monsters still do way better here. There are possible exceptions (Cornealus, Spark Pixies) but you wanna have some read on opponent to do it. Playing this mode like normal is fine and changes are quite subtle (you can play high health ranged unit as secondary tank or such things) Perfecting this rule is actually quite hard, but mistakes are not that punishing.
7, ranged + magic have snipe: you can also use composition that does not have any snipe target (tank or two + opportunity/sneak melee monsters + possibly throwing something like cube in last position), normally this is not good comp, but it counters "common sense" compositions like you mentioned pretty hard.
9, armored up: or use summoner/monsters that shreds armor and go melee, since earth splinter also have unicorn with void as tank and armor shred on summoner they are probably best for this strategy, throw in 1-2 silence monsters for auto win vs basically any magic comp.
11, melee mayhem: do not use monsters with sneak, they tend to split your focus fire, which is horrible. opportunity is ok, but not as good as in normal matches, its actually kinda neutral. Inspire, Demoralize, Thorns and armor shred have higher value, other than that brute force approach with just melee works well most of the time.
12, every monster have double dmg vs stunned units: not "every monster have stun"! So quite obviously monsters with stun ability goes up in value.
wow! thanks a lot for taking the time out to share these strategies and corrections. Will update soon.