the towcable was an excellent idea, the walker couldn't move his legs anymore and felt, they were gonna use this tactic again, but the snowspeeder was destroyed before it could shoot his harpoon

Luke opened a hatch with his lighsaber and threw a grenade in the belly, I think where all the machines and so the at-at exploded

cause at first they didn't know how to stop the at ats, else they never would shoot on them with blasters, only then they knew the armor is too strong for blasterfire, so they had to try another tactic