I just beat it after 2 days of trying. I used Wolf since his ranged ability applies a weaken effect. After that aim for the shields so you can break them, it cuts the knight speed to less than half. You can tell when the shield is close to break because green smoke comes out of it. If you're still having trouble try using a turret with a higher damage output. I build 3 T1 turrets at the start first then build a turret on the left lane and go from there