3 stars with 1 line freezing traps, 2 lines of spikes, 1 line of barricades and 4 lines of archers, all fully upgraded. Bring down the drakes with fireball-iceball-fireball (maxed) combo, and keep those barricades up. Whenever I got some breathing room from the drakes, I fired one or two iceballs down the mass, trying to hit the elementals. Tried a few other tactics from the other comments, but I found this one was the easiest. Whenever I had to save up some mana, I just fired the cannon (maxed) into the big group.
 "Siege Knight"){kind=icon}
 "Penguin Massacre"){kind=icon}