Colossus, just hit skill 1 over and over again it has aoe dmg so it does the trick and stand far away from spawn point. End game or how it is called, go without the walker avoid fights, whenever possible kill 1st walker, continue, kill second walker, go back get a walker, go till you can. Second phase, mount the walker right away and proceed. I found this workaround by trial and error. Enjoy 😉. On Voss just play it safe. There is a workaround too and I found it on my second death, last walker is easy to kill.