Extra note: Upon reaching this stage, you’ll pretty much have gems to purchase at least an extra hero that is worth 1500 gems. If not, try fulfilling Quests in the game in order to collect this much to purchase Bolton or Masamune. At this point, Bolton is our best choice for crowd control. Masamune is a great alternative but is rather tedious to utilize. Nonetheless, it is your pick.
Campaign Mode strategy: Start the level with two barracks to hold down the mob, and a cannon on site at the top of the triangle (as seen on the image). You can’t help it but have some of the mob get past through your choke points so put up at least 2 barracks or archer towers near your bases or at least past the triangle on the center. Reserve for Fee’s feral wolf on the start of the 2nd wave as the bandit will appear this time. You may choose to target him with Lancelot as well.
Around the 3rd wave, you should have placed the two barracks near your bases, and put up additional fully upgraded cannons at the bottom of the triangle at the center. Let Lancelot help hold down the choke points by placing him near the enemies’ entry point. Around the 4th wave, you may choose to put up additional barracks near your bases to secure them as a lot will get pass through your choke point.
Add a wizard tower to clear out enemies on its line of sight, and purchase its haste buff and let your melee units benefit from this by positioning them in its proximity. As you reach the 6th and 7th wave of the level, put more fully upgraded cannons to help trim down the incoming horde. This should do just fine in order to obtain the 3-star rating.
Legendary strategy: Start off the stage with 3 wizard towers on top of the triangle and 2 barracks to serve as choke points. Have Lancelot secure the left lane and the Bolton the other lane. Put Fee at the middle of the triangle and summon the wolf wherever it is needed. Upgrade the wizard towers first with the haste buff and the barracks as well. Secure two more barracks, 1 each near your bases, and an archery tower at the bottom of the triangle. This should be plenty to hold off the attack.