3 Rows of Archers
1 Row of Walls
2 Rows of Spikes
1 Row of Freeze Traps
Then alternate between the Cannon and the Shot Gun. Nothing stands a chance. The Traps can deal with the Ogres, Skeletons, Ghosts, Orcs, etc. everything besides the Fire Elemental and Drakes. You may need to place extra walls. But with this set up you can beast the last level.