zam is really hard to build around without magic guard imo. skarm/forre as a defensive core is pretty dong, even more so with potential probo. i can see wanting spin over defog if you can reliably set hazards, but lefties skarm and forre are just mag bait. skarmbliss is meme af but i mean it works. spikes/roost/defog/brave bird skarm with shed shell, and rocks/wish/twave/ice beam on blissey.
mag is ran mostly as a trapper, which is how you should use it here, because ferro/forre/ opposing skarm would give you a pretty hard time. i would personally run scarf on this team because of how important it is to dispose of scizor to allow zam to shine. granted you lose the ohko on ferro and its a roll on spdef forre (guaranteed at 2 spikes, or 1 spike + rocks), id say its worth.
id replace hax with scarf mence. takes care of ttar, every other dragon, another answer to steel types, and a shaky volc check. just need to pivot into it. intim is always nice as well.
lastly id replace kingdra with gyara. another ground immunity, another intim, and unfortunately another rocks weakness.
https://pastebin.com/epFJ0H76
its not the standard MMO fatness, but its a quick build, and meh, thats waht RMTs are for.
also took the speed off skarm since no taunt.