This should be a warning for people who want to take down NPCs lvl10 and just read the forum.
First attack :
Lost almost everything. Eventually I conquered this one and the Hero's Attack was 64.
Second attack :
Lost half the army. Hero had attack 159 in the first attack, 164 in the second. Seems to me that everytime I'm attacking a NPC, my losses increase when they should decrease.
So everyone be careful, most of the people who are giving battle reports have done this for quite some time and have strong heroes.
Needless to say that everything at the academy is at level10.