This level is particularly tricky and you really need to actively move your heroes from side to side as otherwise your towers probably would not be able to cope alone.
Check out the screenshot below to see our starting layout.
Level 13 - Starting Layout
Weirdly, starting with two upgraded wizard towers worked really well for us.
As the level progress we added a few more wizard towers to try to cover both sides.
Level 13
By now we had added some golem towers which worked really well with the wizard towers.
Level 13
The final wave below shows an example of good hero positioning as all of the enemies were on the left side we put our heros there too. If you are slow moving your heroes around on this level then it will be difficult for you to get three stars.
Level 13
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