It's a factory. There are robots there. I havn't exactly been reduced to a gibbering mess trying to make sense of that, to be honest.
There are lots of hazards the robots like to stand in and they're often at frenetic knife-fight range. Those of you who were using bombs or alchemers for your construct-killing needs may wish to invest in a sword for construct killing.
Well the thing is that Germlins build constructs so it makes sense. If a Gremlin boss does come around it'll probably be the king himself or some kind of super minion. The Flamethrowing Gremlins do elemental damage, I'm not sure about the demo gremlins but an explosion would lead me to believe they have elemental damage too.