So the hint at the beginning says Mr. Legs has wires under it's head that I need to rip out. 
 
I've tried everything, I'm not sure how to achieve this... The closest I get is foaming his legs so he can't move

Foam both his legs, then hookshot under his head. Do this three times then it'll only take like 2 rockets

There's an ammunition box of foam on the right side aswell.

" Foam both his legs, then hookshot under his head. Do this three times then it'll only take like 2 rockets "

I think I must have accidentally sequence broken this part. I had triple jump yet no hookshot.

I couldn't suss out how to get at his wires either so I just hung from the ceiling on my hook and chipped awy at him with my rifle. Took ages but he went down and then as he was exploding and I dropped down the B button prompt showed up for the wires so I ripped them out for added punishment.

I stayed in the general vicinity of him, get too far and he pelts you with bullets.  I dropped foam on his legs and also in the back of its head where that light is & just shot missiles at him while avoiding his freeze grenades.  Be sure to keep foam up.  After my last missile he was down to about 10% and just spammed grenades and end of story for Mr Walker.  After reading the posts here though, I've realized that this is the fucking hard way to do it as it took me about 7 tries.

wow.  all i did was hookshot to the roof and shoot the top of his head area.

He glitched and was shooting on the same spot, I was behind him so i was just holding the Right Trigger and he went down after some time.

I dunno my strategy would probably would work on insane.  Only time I ever got hit was when I initially tried to get on the roof.  Other then that i never got hit as long as when i fell on top of his head I reattached to the roof before he ground stomped.

I am glad this existed. It came in handy.