I have built an arena, and it was a let down. Wildlife doesn't attack goblins, and my dwarves are too strong for goblins.
There seems to be another problem, but I'm not too sure of it yet.
Example one, a recent post.
http://www.bay12games.com/forum/index.php?topic=33553.msg514615#msg514615He claims that 3 animals took out 24 goblins. 24! With armor and weapons!
Then we have Captain Duck's youtube tutorials, and in one of the movies he has an in-betweeny video of an arena fight where he pits about.. I think 3 dogs versus 8 goblins, and all 3 dogs survived. I can tell you, in a normal ambush, my wardog (acting as a gate guard) can barely take on one goblin.
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Edit: I think this is the video. Not quite the numbers I thought they were, but no wolves/bears/dogs were killed (except for one wolf that was injured when released from his cage.. Ive had that happen to a dog. Quite weird). All goblins got horribly mauled. Though good to see that the more aggressive wildlife attacks goblins.. unless Captain Duck modded them to be war trained. Still not too sure about all that.
http://www.youtube.com/watch?v=7zxW_rZFBV0&fmt=18===
Then we have my own experience, and one of them is in my gauntlet. I unleashed about 15 goblins to run through traps, release two war dogs and then a few more rooms to their freedom. When they triggered the dogs, about 10 goblins ran through. The dogs killed 7 goblins, and 3 survived (they ran through). The dogs were
not injured. The goblins just ran.
What's happening here? All I can tell is that the goblins will run, run and run. My theory is that they were part of an ambush or siege squad that was forced to retreat because of casualties. a member was captured, but is still in "retreat" mode and will do so even when put in an enclosed arena.
None of the caged goblins I released have fought back so far.