Oh, another great idea: just build a gigantic tower of dirt with you on top and make sure there are no mountains nearby, that way no mob will be able to reach you.
This gamemode would need some additional limits for the miners to work properly, or give the mobs more power and introduce ghasts, just like Epic_Morph mentions.
Exactly what I tought:
1) Build a tower
2)Stand on the edge of the top block and expand the tower
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Edit: I found this image with different kinds of soldiers. Which one do you want?
http://fc05.deviantart.net/fs47/f/2009/220/3/6/Helghast_units_by_avenger09.jpg
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OMG. NOTCH ADD THIS!
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Simple as that, a lying door
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Simple as that, a lying door
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Simple as that, a lying door
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Simple as that, a lying door
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Simple as that, a lying door
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Exactly what I tought:
1) Build a tower
2)Stand on the edge of the top block and expand the tower
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3)
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4) Profit!
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Assuming mobs can build, of course.