The strategy that I've used was a frost and a nova or their prime counterpart with a trinity keeping the energy flowing and a rhino using roar to boost DPS. I'm trying for Loki prime systems so we might have to go 20-30+ waves. It's simple with this setup. Rhino boosts team damage by 50%, nova nukes everything on screen, frost puts the objective in a snow globe and trinity keeps energy and health up. I am on ps4 if anyone is interested It has been brought to my attention that limbo is a better defender that frost so a limbo would be welcome instead