Basically after they open the thing it's tribal warriors VS some ugly sci-fi monster that was designed to wreak havoc amongst armored high-tec soldiers with rifles and movement detectors.
My bets are on the tribal warriors. Sci-fi monsters might be able to survive laser cannons and sonic blasters, but they always fall prey to some simple sneak attack involving rocks, sticks and such. Besides - how is a futuristic android/mutant/cyborg going to survive in a primitive, non-technological wilderness?
Good point! But the monster inside is not high tec in its nature nor does it depend on any fancy stuff to survive. It's quite primitive - something like "The Alien". But with strong stealth capabilities, skin that normal bullets wouldn't penetrate and never ending hunger for blood. Tribals are pretty screwed unless they unite and come up with a good plan. (burying under large amount of rock sounds fun indeed, and good for sequel, too)
Well that makes things more interesting... a self-sufficient indestructoid versus a bunch of tribal people. It will probably slaughter hundreds, cause the rest to flee in terror, leaving the monster in a land where none dare to travel. Generations later, when the tales of old have become legend, some rebellious & naive youths disobey the elders and travel into the forbidden land, intent on proving the old tales to be myth.....