1 word, Impossible. You don't get enough earning to get anything within a decent time frame. Also these spawners... seriously? 2-3 at a time on one wall and the AI of the troops and mortar are like the queen in COC "lemme shoot the minions forever and never attack the spawner." Better AI's on troops and more income would make this a perfect game. Seeing how the Creator hasn't updated nor responded in almost 6 years, I guess this is just a rant lol.
Whoever came up with this click and drag system, put yourself in a well and seal it off. Challenge 4, is almost impossible and 100% luck. For instance, shield goes within 2 cm of the dragon and the dragon just lay waste on sword, orrr sword decides to do EXACTLY what you want and dragon still shoots him instead of the shield. Seriously, waste of time man. Appreciate the game but next time add in a double control system eg. awsd for 1 bot and arrows for the other, not click and drag.