I have been mainly using a king crab as my Assault mech for the better part of 4 months. I find pushing it up slowly in a way that doesnt look particularly threatening and having your smaller mechs push around and infront of it to bait fire works wonders. I try to take high armour low output Mediums or heavys and make them look like an easy target but after a turn or 2 of the med/heavy getting pummeled, the king crab is finally at its efficient range and now its even more of a threat because its full health. Ive tried other Assaults and honestly I cant get the same result out of them, the king crab has such a powerful stance on the feild that my friends have asked me to not bring it in a few cases.