Three post I wanted to remind you guys about:
First - if you are the one who is Attacking - chances are you will be matched against a stronger army, but if you are defending - are are guaranteed to be matched against equal or weaker army. So especially if you are using Be Brave feature and attacking - you need to be prepared to face Royal Dragons.
Second - there are some specific anti-Dragon troops (same applies to other monsters such as Ogres). Here`s some pointers:
-archers are ranged troops are mostly useless against Dragons, unless they are level 5 with attack upgrades, don`t bother
-Dragons are 100% immune to fire damage, so using fire arrows or trebuchets is again useless
-Heavy Cavalry - Mounted Grand Masters, Mounted Slayers, or Mounted Knights - work great, but you really need to swarm the Dragon. Light cavalry is not that good.
-the BEST counter unit is Impaler, Sentry and Halberdier - anything with a pike. Just be sure to attack in Loose formation so that fire spells don`t kill all of them
-Bring Elven Warden units with you - as they have area of effect spells that completely eliminate fire
Third - and most important point - the army you are matching against a Dragon typically costs maybe 5000 gold, at the very most. Royal Dragon for example costs 120 influence, which is around 80,000 gold value. So if that player loose his Dragon his loss is much much greater that yours. ALSO - if you do kill the Dragon you will get something like 20-40 points of Wealth in return, so think about it as a gamble with very high steaks on each side.
And finally a quick summary for the new players: "Always bring Halberdier, Sentry or Impaler units with your army. And in PvP never use Be Brave, and better yet - never attack, just defend"