Left 4 Dead 2, like any game, has loads of code/assets that ultimately went completely unused. But some of them are accessible via use of console commands (often in conjunction with sv_cheats 1), letting you see and play with cool beta content!
1. Hidden reload for the Hunting rifle. At one point, the hunting rifle had a much more complicated reload before Valve changed it to something shorter and simpler. But you can still accidentally access the older reload by holding a non-inventory item (like a gas can), throwing it with m1 and immediately shoving with m2. No, I have no idea why.
2. The Riot Shield. The riot shield was a fully modeled and textured weapon that Valve just didn’t add into any official campaign.
Once upon a time you could get it by simply activating cheats and typing “give riotshield” into console, but now Valve set maps so that they only precache certain melee weapons. This mod can be used to bypass this, however, letting you see for yourself why Valve nixed the weapon. Its swing is cramped and tiny like the nightstick and it visually obscures half your screen, definitely the worst melee weapon in the game.
3. A bonus map. Left 4 Dead 2 comes with a one-map campaign that you can only access via console with “map tutorial_standards”. Here’s a guy soloing the map on the hardest difficulty, which trust me is not easy to do:
The map is actually a scrapped finale for Dead Air, and is also present in Left 4 Dead. As the name implies, Valve kept it in as a sort of sample campaign demonstrating all the basics of a map, for the benefit of modders and mappers. You can read more at this wiki page written almost entirely by me.
4. The Leaker. There was a scrapped Special Infected that Valve was testing long enough to be accessible via console. If you create a versus campaign (and set “sb_all_bot_game 1” if you hope to play on the Infected team) you can use the command “boomer_leaker_chance 100” to spawn Leakers instead of Boomers, and they are weird. Invulnerable to traditional damage, the Leaker can implant himself in the ground and explode, dealing knockback and leaving a puddle of fire that deals damage to unfortunate survivors. If that doesn’t sound super remarkable, now you know why Valve cut the Leaker.
Leaker Madness is pretty fun though.
5. Third person view: At some point, Valve was toying with adding third-person to the game, and while they never got it to work particularly well, they didn’t even blockade the final result behind sv_cheats 1. You can jump into a multiplayer campaign right now and type “thirdpersonshoulder” into the console and enjoy your new blanket accuracy penalty.
If you’d like to adjust it so that the bullets actually go anywhere near the crosshair, this is the mod I use. It’s missing that cool over-the-shoulder feel but it gets the job done.Though it’s blocked in Versus mode because Valve thought it makes it unfairly easy to see around corners, and they’re totally right.