Shouldn't it have the "massive" trait? I can't imagine how this big golem could go inside a building, it also makes him VERY strong.

I was looking for an errata, but couldn't find one.

Well, as far as I can tell from the card it doesn't say 'massive'. But I totally agree with you that it's kinda weird not seeing the 'massive' trait on this unit, as it is.. well MASSIVE. Maybe it has something to do with the fact that it's ranged... Or when looking at it from a 'use your imagination' perspective I suppose one could argue that siege-machines/devices/towers originate from a city/town... Apart from that it does have a movement restriction listed at 'Behemoth' which states: "If this unit moves during your Move Step, it cannot perform an attack this turn. This unit ignores units when determining line of sight." so maybe the Dev's thought this would be enough movement restriction to keep it balanced. Although.. when it's moved into a building eventually you'll probably keep it there as an insane long-ranged siege beast. IMO Siege Golem is like an improved & ranged version of the Uthuk's Chaos Lord, when comparing stats.

So I'm still kinda surprised not to see the 'massive' trait on this dude. But then again I always play Uthuk so every Legendary Daqan unit ruffles my feathers.

You can still kill it in close quarters, but yeah, it's a tough beast. Hence, better protecting the buildings (puttng one of these into a building could require some time, tho)