Hahaha I'm SEVEN HOURS late so funny
FUNNY PHYSICS I HAVEN'T SEEN ELSEWHERE VERY OFTEN:
In point insertion, right after you see the strider and before you enter the playground, head down the alley towards where two citizens are being held up by metrocops. Let's call the first one Tony. Get Tony to aggro you, then go stand on top of the very edge of the dumpster behind you. Typically, if Tony hits you, Freeman gets knocked tf out. However, that only happens inside a trigger volume, and that dumpster sits just outside aforementioned trigger volume. So, when he hits you, it's just a normal stun baton hit. If you're in the right spot on the dumpster edge, the stun batons knockback SHOULD cause you to "trimp" (not really trimping, think of it like a reverse edge bug), and end up launching you. It's very finicky but I've managed to boost myself up on top of the buildings before. Similarly, if you're mid-air when a metrocop hits you, you gain a lot of momentum because the knock back isn't absorbed by the Source engine "friction". That only works horizontally though. If you wanna go vertical, the dumpster or some similar prop is necessary. (P.S. I don't know if this works on newer versions, I can only test on an old 2010-ish build available on Xbox as I don't own a PC. Apply that to everything else, k?)
Next up, if you go to the chapter sandtraps and go to the bridge section, should you kill a combine on a catwalk, you can use the crossbow to make his ragdoll "freak the fuck out", for lack of a more scientific term. All you have to do is make sure there's a wall below the catwalk, aim at it through him, and fire. The bolt will catch his ragdoll and go through the catwalk, then stick into the wall. At this point, the bolt TRIES to pin the ragdoll to that wall, but since that ragdoll can't get through the catwalk, so it just kinda...Freaks the Fuck Out™.
Next...Bathtub homunculus. So, YES, weird name. I know. However, I don't know what else to call it. Basically, if you go to the battery puzzle(you know the one), and shove a rollermine into a bathtub(just slam it in the back end of the bathtub like you're dunking a basketball), the physics engine REALLY doesn't like this. Effects range from: launching you(death guaranteed), bathtub car for rollermine, launching the rollermine, and literally just floating there. Menacingly. Don't ask me what SOURCEry governs this thing, I couldn't tell you. It has a mind of its own and just kinda does what it wants. All hail the Rollertub.
Probably more I forgot but whatever.
There DOES exist a backwards compatible Xbox 360 version for HL2, as I said before. It's called The Orange Box. Unlike the Steam bundle version, this comes on a disc which uses a built in launcher for all of them. It's similar to the Master Chief Collection in how this is handled. The Orange Box's latest update is older than hats in TF2.
There also exists an arcade version of HL2, released only in Japan, as well as an original Xbox version.
Moss growth was also a thing at one point in development, apparently.
So, first, metrocops. Metrocops use the Californian state police codes. Well, a modified version of them. Combat dialogue like "I'm 11-99" is California police talk for "Everyone in my squad is fucking dead." Why they're using this in Bulgaria? No idea, but I headcanon that the Combine aren't aliens, but just a group of Californians gone mad with power.
In addition to that, here's some radio translations for the Combine. The ones I remember, anyway.
Cohesion: Consciousness and/or life.
Squad Cohesion: Exactly what it sounds like.
Verdict/verdicts: Bullets/beatings/maybe fines?
Malcompliance Verdict: A beating.
Ration(s): Food, typically used as a reward for good citizen behavior.
Artificial Reproduction Simulation. A reward for good metrocop performance. You can probably imagine what "Reproduction Simulation" entails.
Family Cohesion: Used in context of metrocops as a punishment. If a metrocop is killed or otherwise fails, the Combine seeks out and executes their former family.
Anticitizens: used as a kind of wanted list. Anticitizen-1 is whoever has the biggest bullseye on their back.
Biotics: Headcrabs, barnacles, antlions, etc.
647-e reading: Possibly some kind of surveillance or radar system used for tracking?
Outbreak: General chaos. Situation FUBAR.
Probably more I forgot. All of these definitions are derived from in-game radio chatter. I think it's actually really cool that they react to threats with the according codes rather than just spewing voicelines at random.
Only one video I've seen addresses this next concept, and coins it as "Civil Confusion". CC refers to how citizens are randomly moved city to city, most likely to prevent them from organizing rebellion by making plans.
Crab and mortar synths(cut enemies from the beta) can be seen in the Citadel heading up to Breen's office, and appear to be mid-deployment. I know this is well known, but it implies that they ARE used, just only in response to uprisings like the one in City 17.
Gunships and dropships seem to have been originally(before the Combine did their thing) both been aquatic species. This is evidenced by the presence of whale-like fins.
Advisors, or shu'ula'thoi, were originally a species of lucid dreamers. They would hibernate for long periods, and had a collective subconscious that they used, essentially, like the internet. At some point, a "virus" spread, turning every dream into nightmares of death and destruction, inducing physical sickness in the sleeping advisors. This was up until the Combine came along, and did their thing. The advisors are not the highest class, they're just lower-middle management. This is all collected from the "Breengrub" account on Twitter, run by Mark Laidlaw, who wrote the story for HL. Its canon status is questionable, as Mark described it as a Dr. Breen fanfic, so do with that what you will.
This isn't ALL my HL2 knowledge, but a good chunk of it. I'm stopping cuz my fingers hurt.
I wish you a very foreseeable consequence.
