If you somehow managed to not see the film yet, please avert your eyes. This is full of SPOILERS.
Yes, it is over the top and probably the road to ruin for your campaign, but I dissected stats of the creatures seen in the 2008 film "Cloverfield" found here and translated them to Basic Roleplaying Rules.
Without further ado, I am pleased to introduce "Clover" (head to tail length 365.8 meters and weight 5806.4 metric tons) and his accompanying 2,000 parasites. Of course, no good can come from actually trying to fight Clover unless you have access to a neutron bomb. As in the film, most of the "interaction" with humans is with the parasites, who are relatively easy to kill one-on-one, but pack a wallop if they manage to bite you and/or if they are acting in concert.
Clover, Large Scale Aggressor and Reality Video Star
Damage Bonus: +20D6
Armor: 100-point skin
Attacks: Stomp 50%, 20D6+Damage Bonus
Bite 45%, 20D10+1/2 Damage Bonus
Evade Heavy Artillery 50%, Get Enraged 75%, Induce Shaky Video Camera Filming 90%, Listen 20%, Sense 20%, Spot 20%, Terrify Yuppies Witless 90%
1/1D8 (and you never get used to seeing it)
Notes: I addition to being able to move relatively quickly and use the cover of buildings (35-55 armor points in the concrete and steel canyons of Manhattan), the creature has a high resistance to projectile weaponry. Shells from M-1 tanks, AT-4 rockets, 80 Mk 82 bombs and other high powered ordnance failed to do anything other than aggravate the creature. In the film, it appears to have been killed in a passing reference in the final helicopter scene to the HAMMER-DOWN Protocol, which apparently sacrificed Manhattan to kill the creature.
Clover Parasites, Human Scale Parasites
Hit Points: 7-8
Damage Bonus: -1D4
Armor: 1 pt. chitinous shell
Attacks: Bite 30%, 1D6+1/2 Damage Bonus (Bleeding plus POT 18 disease which runs its course so quickly you should treat as a poison with the effect of weakness and pain and graduating to hemorraghing and convulsions in progressively debilitating stages for 2D4 turns or 10-40 minutes)
Grapple (Hold) 30%
Skills: Climb 85%, Dodge 50%, Jump 85%, Sense 75%, Stealth 80%
1 Pincer #1........1-2
2 Pincer #2........1-2
3 Pincer #3........1-2
4 Pincer #4........1-2
5 Leg #1............1-2
6 Leg #2............1-2
7 Leg #3............1-2
8 Leg #4............1-2
9 Leg #5............1-2
10 Leg #6..........1-2
Notes: The creature is accompanied by 2,000 parasites that are about the same mass as a dog. They have ten "legs," which are six spider-like, double jointed legs and four crab-like pincers on the top and back of its body used for grasping and climbing. They possess large mandibles, pale grayish skin and innumerable black, soulless eyes. On first inspection they resemble a giant spider or tick.
They attack with pack coordination and prefer enclosed spaces for trapping and surprising prey. They can also detect prey from afar, by an unknown method.
Their saliva cause the victim to feel disoriented, bleed from the eyes, and finally cause a Class IV hemorrhage.
A fumbled First Aid or Medicine roll results in pouring water on the wound, which speeds up the violent combustion resulting in 2D6 damage.