I would love to see
Unique bosses like a big slime that divide itself in 2 or 3 everytime its HP reach a half. A big robot that fire laser bean on center to hit every monster you have, on the top and botton you have to destroi It's arms, after that your units from botton and top that survived can join the mid lane.
Big bosses that uses all the 3 lanes at the same time, attacking and beeing attacked
Bosses would be Awesome!