The trials are intended as a very hard and challenging level. You either need brute-force and huge amounts of HP, or a clever tactic. There is already a discussion about the trials ongoing, which is, at the time of this post, on the first page and as such easy to find with a little bit of effort.
http://discourse.codecombat.com/t/has-anyone-beaten-the-trials-on-a-free-account/2683?u=j_f_b_m