[quote=@mcpop9]
Metal gear focuses a lot on nano machines.
[/quote]

Not to the extent I'm thinking of. I'm thinking of a mech made entirely out of Nanomachines. Which means they can make almost any weapon much like the aforementioned series I listed. The downside of this is that it also means the mech would ALSO have some scary regenerative abilities and the other terrors of Nanotech, IE, Mass can be converted to other mass a-la FMA. The problem is I'm more interested in the regenerative ability and make its combat more melee based and ranged weapons can only be used at a severe energy cost or if an external power source is used. But I'm not sure if you think thats ok or not. 

Their weaknesses would be basically whatever it took to kill that terminator in I think the first movie? You know, the one who was made of liquid metal. Either that or a kill code.