I don't know if luck is really in it. I used mermaids, gnomes, centaurs, minotaurs, phantom armors, and used invincibility and beat it twice using those. The strategy is to move your hero in the middle and hold off the goblins etc. until your army reaches max then move all your troops forward when you get near the invincible goblin use invincibility and he will simply get knocked back while you destroy the castle.
yar Stev0 had a good plan that I beat the trials with with this: "rekojssl. Lots of units and the invincibility card... just bumrush him (send everything at once) once you have full troops. Best ones are the ones the developer suggested which are mermaids, dwarfs, phantom armor, and minotaurs. I chose succubus and centaurs to go with them. Spells, you can choose whatever you want except you need invincibility and comet shoot. that's about all there is to it."
Listen guys they probably are going to give badges to this game especially since its one of the top 3 in monthly. flooding comments with this stupid thing is not needed right now.
Narwhals is old. It has little to do with the song.
Back on topic Hero Interactive your games keep getting more and more original I believe you have outdone yourself on this one.