If I recall right, the only exlusive weapon was the Flamethrower, but they also added the missile Warthog. Might be forgetting some other weapons though, as I never had the Xbox version.

I had some fun when I was younger modding the demo. The only content stripped out of it were the levels, so there were all these custom versions of the Blood Gulch map floating around with Ghosts and Scorpion tanks, etc.

I liked messing with weapon properties. Had my own temu/wish.com "cursed halo at home" long before it was a real thing.

• Sniper rifle fired plasma grenades, and you could do fun stuff like stacking two so the first would throw the second into the air and the trail and explosion made it like a flare.
• Shotgun fired a spread of frag grenades instead of bullets, and pushed you backwards a bit.
• Pistol was more accurate, slightly faster, much less damage, and pushed whoever got hit back a ton. You could easily juggle someone up into the skybox with it. It pushed vehicles too.
• Rocket launcher fired a massive ball of rockets that would lag everything.
• Flamethrower fired rockets instead of flames, with a much higher ammo pool, but no other changes. So rocket sprinkler.
• Fully charged plasma pistol fired a Scorpion Tank shot. I think the non charged ones homed in to a stupid extent.
• Chaingun Warthog fired needler rounds with an increased lifetime.
• Assault rifle worked as area denial, setting an area in an orb shape around you on fire.
• The plasma cannon thing would spawn a Scorpion tank over your head, crushing you.
• I think I turned the needler into a shotgun blast thing, but it still fired needles.
• I think I changed the elites' plasma smg thing to start firing slowly but "rev up" to stupid fast speeds, and then the cooldown hurt your shields?
• There was something that would call down a larger version of the plasma cannon projectile from the sky, with a larger explosion radius and a stupid big/strong pushback effect.
• Vehicle crashes called the same kind of system as a projectile hitting, so you were effectively "shot" with a vehicle impact "bullet" as a rider if you crashed too hard. Congrats that's now a frag grenade explosion. That one was shamelessly stolen from a tutorial.

That's what I remember at least.