Any tips for 5* laser show

[Immortal]

Congrats!

[scorcher117]

I finally have it it was just a case of using freeze ray, blizzard and heroes to slow the enemy down and once there is a lot I got a frenzy by freezing the enemy's and then it was rather easy to just win I used lvl 9 trolls. I now have 100% in the game. Every achievement.

[scorcher117]

I have every single star in the game except for 2 in laser show I need hard and bonus objective, how am I suppose to do this, hard if I keep trying ill probably get it but and 20 kill streak on this mission seems impossible.