This is an interesting challenge in many ways Ninja Tower is.
I used Kiril +18, Freya +18, Frida +20, Jott +20, Vela +7. I used a few minor mana pots along the way. I found Jott to be the key here to boost those tiles and Freya for the minion damage since so often I was hindered by the healing block.
I opted not to use Gullinbursti as I was too worried that bosses would steal the buff.
I’m not in a rush to limit break anyone. Frida would be my top choice as my current best Ice hero and being so key in so many aspects of the game. Jott and Kiril are the next two I’d want. Kiril is my go to Ice healer. I don’t use Jott other than score based things (titans, challenge events, ninja tower). I’m not too worried about the three stars. I find top 10k easy for challenge events and top 1k almost impossible for me, so I don’t need them there. It would be nice to do better in raid tournaments to earn more LB.