Including monsters puts me in mind of the Numidium in the Elder Scrolls series - a giant golem, essentially, used by the Emperor to conquer much of Tamriel. Imagine a king with an iron golem - how will any army or any fortress stop his attack?
God dammit, I tried my hardest not to say this in my first post, but now you've tempted me far too far.
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Gundam Fight! Ready...GO!
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Stealthy Snake avatar by Dawn
Lack of images by Imageshack