Well, after watching
Predator for the ump-teenth time tonight, I decided to put way more thought into the lead character than all my other viewings combined!
I don't think there was a "transformation." What I saw was a soldier with skills, talent, training, experience and extreme physical conditioning who brought all that to bear on his situation.
Sure, the traps and weapons he built were "Boy Scout shit" (according to Carl/Dillon), but from the time they lost their first teammate, Arnold began receiving and gather clues about the enemy's capabilities and limitations. Without dissecting all the scenes and dialogue, he learned:
1. It uses camouflage similar to a chameleon.
2. It bleeds, so it can be killed. He also knows what that blood looks like.
3. It hunts for sport, which is why it didn't kill Anna who was unarmed.
4. In Anna's village, in the years when it was very hot, the men would be skinned or worse, that this thing hunts humans and has done so for a long time.
5. It can see their trip wires, but can't easily see traps and triggers made of rope, vines, limbs and rocks.
6. It uses the trees to gain the "high ground" advantage, and can travel through them to avoid trip wires.
7. It has advanced energy weapons that use laser sighting (the Predator shot at an animal in a tree stump while Arnold was watching -- right after he first got muddied up).
8. It could not see him with the mud on him, which indicated its vision was heat-based -- probably in the infrared spectrum.
9. The camouflage capability could be interrupted, like it was from it falling in the water.
He then decided to make the big tree in front of him his base where he would set traps and areas that would make it easier to see it. This way he gained the home field advantage -- let the hunter come to him. He also used vines so he could take the high ground. He used fire and more mud bathing to "blind" it. He was without his normal weapons, but had his knife and some rifle launched grenades. He used the gunpowder to make exploding devices: arrows, spears and a "grenade pouch" around his neck. Luckily he also had some stick matches. He was very resourceful, which indicates a lot of time spent in survival training and practicing it in real life.
A lot of the traps were designed as anti-personnel contraptions. I'm sure they were a combination of survival know-how for finding food as well as devices used in jungle warfare throughout history: pits with punji sticks, large snares to toss you into pointy branches, etc.
I think this all falls under the category of "improvise - adapt - overcome." He was able to gather some intel on his enemy, through necessity and his previous success of using natural resources for traps. After analyzing the enemy's strengths and weaknesses, he was able to apply that knowledge and his skills to gain an advantage.
Much of this is within the wheelhouse of a soldier's knowledge, not that of a game hunter. Although the two worlds overlap, hunters are not often busy trying to survive attacks from the very animals they are trying to hunt.
All in all, I think the musical score "makes" the movie. Reminds me a little of the score behind the Eastwood western, "Hang 'em High."
I did learn something new I never noticed before. The same actor, Kevin Peter Hall, played both the Predator as well as the helicopter pilot flying the chopper coming back for Arnold. He looks out at the mushroom cloud and says, "What the ... ?"

I learned most of my wilderness survival skills from my Scout Master, who happened to be a former Green Beret. Go figure.
