Slender fortress is a Gamemode that is pretty much Slender but in Team Fortress 2. The goal, like the source material, is about collecting eight pages/gas cans, and dealing with a boss that is always hunting you. That's Slender Fortress in it's esscence.

The bosses can vary in a large amount. On most maps, the default boss is Slender, and every 3rd round (citation needed) is a random boss. There are also special rounds with modifiers inbetween, and I will cover them later. Rounds are roughly 5-10 minutes long, and you will be placed in a round depending on your queue points which you earn at the end of each round.
There are specific bosses, which I will list

• Slender (default on most maps)
  
• The Rake (frost run's default)
  
• Suicide Squidward (random boss)
  
• Hell Knight (random boss)
  
• Animatronics (Five Rounds's default boss)
  
• Woody (random on arizona, possibly others)
  
• Kate (abyss random boss, in conjecture with Slendy)
  
• Guardian and Hellknight (Sector Six/Random)
  
• Patriarch and Fleshpound (alpha complex)
  
• Simon (random boss)
  
• Trager/Chris Walker (abandoned, not to be confused with abandoned_tomb, The_ward)
  
• Fire Elementals (arizona)
  
• Fire bosses in general (Ben, Fire Atronarch, Gravity Falls)
  
• Neck Snappers (Weepers, SCP-173)
  
• SCPs (SCP 049, the actual map SCP-083-b, figures inside scp-083-b)
  
• imscared (arizona)
  
• Pinkamena boss(hospice/random)
  
• Tryophobia (random)
  
• Doors (containment breach)
  
• Amnesia Bosses (cellars/mansion)
  
• Sisters (scp_087_b)
  
• Sarah (not her name but I'm not googling it)
  
• MTF/Mobile Task Force (containment_breach)
  
• Sawrunner (sewers)
  And some more I can't remember

Engineer's perk is that his flashlight works longer than usual, and in theory regenerates faster, therefore cowards should use him most often. On the downside, most maps have infinite flashlight, and the flashlight also attracts bosses, so be cautious when using it a lot.
Medics, by their medical background, heal over time. So for bosses that chase you and don't have one hit kills (Rake, Ben, etc) However, your attraction rate is increased to all bosses, so you'll doom others by travelling in groups. (Note, the author does not condone that practice, but I can't stop you.)
Scout has faster regenerating sprint and sprints faster. Useful for evasion tactics, he can run away from most "pop-up" bosses like slender with ease, although chase bosses still require skillful thinking to get away. However, he can't survive damge bosses for long, being so fragile.
Soldier is an average class. He moves slower but can survive more attacks than usual, making him useful against rake and such. His movement makes him a bit more challenging to play as, but not impossible.
Heavy is a tough one. He moves quite slowly, his gloved weapons block the screen, and has a large health pool. His only real use is for maps with bosses that don't deal insta kills. Otherwise, I'd say it's a waste of time.
After years of looking through a scope with unblinking eyes, Sniper magically got the ability to not blink as much. That's his main ability, and really only works when you have a boss that needs a blinking mechanic, such as the Angels or SCP-173. Otherwise, average.
The stealthy Frenchman, the spy has quieter, stealthier footsteps. When crouching, the boss barely spawns near you, and only in mid-chase is it hard to hide again. His voice commands also attract the boss less, but you shouldn't be using them anyway.
The pyro is also average like the soldier. I think he might be able to see better in the dark, but that's just me. Carry out the basic strategy and that's it. He's also flame "proof", so Ben is not an issue.
The demo can run faster than usual when he's spooked. See, when you're near the boss you run faster. The demo does this at around the same spook speed as scout, so good for evasion. Otherwise average.

The basic strategy is what you should do regardless of class or map. It's real simple
One: DO NOT USE VOICE COMMANDS! The faster you learn that lesson, the faster the game gets way easier. Voice commands attract the boss, and should only be used in cases of sacrificing yourself for a friend or someone else.
Two: Save sprint for the end or running from bosses. Sprinting to get to other places wastes sprint, makes you more easier to find by the boss, and is infuriating to sprint-walk-sprint-walk-die all the time when the last page is found.
Three: Use the flashlight sparingly. It attract the boss slightly, but you should use in dark areas at least.
Four: Tell your team-mates where you've searched. It's a bad idea with really short AFK timers (read:10 seconds) but helps in the long run.

That's about it, follow that and you're good.

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