First off, equip Blue Dragon (the woman with spaceship). Next, play 33 Seconds, level 18 which is the ice bone pillars you have to destroy, on casual difficulty. Third, use your hero to speed to the pillars and demolish them. You can even save more time by using her laser beam to insta destroy one of them, as well as using the feature where you can retract her from the field and then deploy her across the other side of the map with the other pillar. This will net you a full game level's worth of loot in 1-2 minutes. This is really useful to get max upgrades and then buy a lot of the extra abilities such Frostbite Warhead and Orbital Strike.

Congrats, you now have 50x of each ability to just demolish those overwhelming waves at the beginning of any Impossible diff level.