Do imps ever do that? I've done over a dozen forts now, and have yet to run into a magman. Lots of imps tho. Plus I was just starting my third spring. I have yet to get a fort past year 6, they normally get taken out by strange flooding, cept for 3 I blew myself while learning how to use floodgates.
I did have a dwarf get close to that spot, and even had a miner dig an inspection hole to the lava just in front of the gates, so if something showed up it would head into the other tunnel, but I saw nothing, and nothing attacked either dwarf.
Least this time I dug a channel to the chasm in the tunnel, just before the last gate fell, so I can bridge accross to the other side. Before that, I just let the lava use the normal tunnel. That miner and his cow got out one end, just as the lava started in at the other. THAT was TIMING!
And to answer someone else, getting enough bones has never been a problem before this map. (This time desert. No game, just big cats. But I have horses and cows breeding, and expect to get lots of goblin bones. Gonna try a "watergun" defense, just for shiz and giggles. No bodies of water outside to make a permanent flood, so just dig channels around the yard, and hose the buggers as they come in! Wonder what the snooty elves will think about me watering a desert?) And I dont like the chasm critters picking off people at random as they cross the bridges. Might only be an annoyance, but its one I can do without.
Magmen tho, thats something new for me. Dont know anything about them yet. But looks like I'm gonna be learning shortly.