One of my favorite series on YouTube is Titsonabullsteam’s Realism Expert Solo runs for Left 4 Dead 2, where he beats every campaign in the game without bots, allies, or exploits.

Recently I’ve been communicating with him because I’ve gotten into L4D2 modding and wanted to help him finish the last video in the series. After watching his entire run again and reliving the amazement I felt the first time I saw it back in college, I was inspired to look into other YouTube series where enterprising players solo Valve co-op titles on the hardest difficulties.

As it turns out, there are two completed series of Left 4 Dead 2 Realism Expert Solo runs, the other by a user named hkl4dplayer. Most interestingly, the two series don’t actually have that much in common when it comes down to strategy beyond weapon choice. Titsonabullsteam in general seems to favor a more methodical playstyle whereas hkl4dplayer is more run-and-gun. It’s also quite interesting how often they choose different places to hold out in finales. Between the two series I know I’ve learned dozens of tricks that I put into practice when trying to survive these campaigns with friends.

If you’ve ever wanted to try your hand at soloing campaigns, I’ve made a mod that plays somewhere between “Last Man on Earth” and what these players have done.

Left 4 Dead in general is the easiest Valve series to find solo runs for, mainly because its the highest-profile co-op dedicated series in Valve’s retinue. User “Natural11001001” speed-ran the entire first game without bots in under an hour, and Zoralink47 has a no-damage run of Cold Stream using only the knife. And then there are solo speedruns, which I could never emulate in a million years:

It gets a little weirder when branching out into other franchises because most Valve games are either single-player or devoid of PvE campaigns. Portal 2, however, has a highly-publicized co-op portion, and user “HS Top” has completed 5 of the 6 co-op campaigns without a second player. “Nine10dan” in his full playthrough catches the campaign HS Top missed and adds a stipulation that the useless second player must be capable of following the path of the first, so no noclipping through all those doors that need two people to open. Unfortunately he does occasionally have to skip certain test chambers if he honestly couldn’t find a solution, but the amount he does solve is remarkable.

Alien Swarm is the other PvE co-op game in Valve’s library, and the aptly-named channel “AsSoloExpert的頻道” has completed all seven maps in Brutal Onslaught Hardcore Friendly-fire difficulty. I admit to not being as familiar with this franchise but it sure looked pretty difficult as he was doing it. Try as I might, I could not find any solo playthroughs of either Half Life:Decay or Team Fortress 2‘s Mann vs. Machine mode. The latter I chalk up to its defense-oriented gameplay (it’s a lot easier to plow through hordes of enemies than it is to kill every single member of an enemy horde before they drop a bomb) but I admit I was surprised I couldn’t find a single Decay solo run. Sure the game’s a bit old and its PC port leaves something to be desired, but I don’t remember it having any curveballs that the ingenuity of the other players in this article and the tools of the Half-Life speedrunning trade couldn’t overcome.