Here’s the setup: T-800 model against a nest of gorilla Aliens with one queen and, of course, eggs in a warcraft the Marines were slaughtered on. Weaponry is mostly intact and unused, as the Aliens do not use tools (at least to fight).
The T-800 time warps into the cargo hold and is pretty much defenseless except for his strength and his amazing durability. An Alien jumps him right off, and knocks him to the ground. The Alien bites through the flesh but is unable to penetrate the hyper-alloy combat chassis, so the T-800, fazed for a while but catching on fast (they never were quick on the uptake), reaches around and rips the Alien’s head off. The acid blood takes off most of the rest of the flesh, but cannot seriously damage the chassis below. (Justification? The T-800 was designed for heavy combat. Its design is basically on the same level as a tank: Slow, ponderous, even a bit stupid, but as tough as the current technology can allow. Organic acids, acids that can be contained by mucous and organically-grown exoskeletons, simply don’t stand a chance against that level of strength and over-design.)
Soon, the Aliens are looking for the T-800 in force. They are agile, fast, and probably have the edge in brains. But none of that really matters as they have no effective offensive against the intruder. Neither their muscles nor their acids are strong enough to do damage to the skeleton, and the T-800 is perfectly functional as a bare chassis.
Eventually, the T-800 finds the armory and equips itself. This is an easy process, as the Marines’ weapons are very similar to what the T-800 was programmed to use. Now the ball is firmly in the T-800’s court: It can basically pick off anything that comes close, and the Aliens completely lack a ranged attack. It is slow enough to let the Aliens get within striking distance, but it is deadly accurate once it gets a bead on the beasts.
And it has infinite patience: It will not make rash moves. It will scope out a room before it enters, looking for humans but killing the Aliens as detrimental to its prime mission. It will quite handily pull off the face-grabbers as they attempt to pass eggs into a metal jaw. It will destroy the queen exactly the same way it destroyed the workers: Sheer endurance and single-mindedness, coupled with a deadly skill with weapons.
T-800: One nest.
Aliens: Closer to extinction.
Next I’ll probably do a scenario where a T-800 tries to infiltrate a dropship full of Marines. That should be interesting to think through.