The Scout has the most weapons in TF2 that cause a status effect called "bleed", which does 4 damage about twice a second for typically around five seconds, for a total of 40 additional damage, should the full duration be effective. The Scout has weapons in both the secondary and melee that do it, too. More specifically, the Wrap Assassin and Flying Guillotine. Two projectile-type (even though the Wrap Assassin's bleed-inflicting ornament is technically classified as a melee, meaning the Vaccinator cannot protect against it and it has the higher critical hit rate that melee weapons tend to have) weapons that both inflict five seconds of bleed on a successful hit. Bleeding also stacks, meaning if you hit both the Flying Guillotine and a Wrap Assassin orb, you'll do double bleed damage. Bleeding, however, is easily removed by healing. These weapons are most commonly paired with the Force-a-Nature; the weapon that gives you higher mobility to come from an unexpected place to do even less-expected damage. The FaN does incredibly high knock-back to those hit by it, of which drastically scales the closer you are to your target. That means, on a light class, since the FaN does over 110 damage on a full meatshot, you can use a well-aimed Wrap Assassin orb or Flying Guillotine to finish off your target. The only class this doesn't work well against is Heavy, solely because of his high health and knockback reduction. Even on Soldier, the potential fall damage could finish him off. If you manage to land both Wrap Assassin and Flying Guillotine shots, that Soldier will not survive unless a Medic saves him, and maybe not even then. However, that means that your melee does 12 damage per hit. Your secondary and melee's special both need to recharge after each use. The FaN does more damage the closer you are to your target, your other two weapons do more damage the farther they go. That means you won't be doing your maximum output at medium range. And if a Heavy catches you off guard, you likely won't survive. The Wrap Assassin does pathetic damage with its melee strike. 12 damage. 36 on a crit. It's critical damage does one more point of damage than even stock for the Scout. The Flying Guillotine means you won't be able to supply more damage if you don't finish your target with your FaN, unlike you would be able to with the pistol or Winger. But the potential combo damage you can do if you aim properly is astonishing, even if it's all only on one person, for one kill. Is it worth it? Is Bleed Scout viable? In my opinion (my PROFESSIONAL opinion), yes. It's good for dealing with Spies, and almost any light class, or any class but Heavy, thanks to the extra movement the FaN provides for you. Despite the risks you would likely need to take to deal any sufficient damage, the satisfaction that landing a good combo provides feels more than worth it. Plus, you do a lot of damage. The Flying Guillotine does 50 damage, then 40 damage in bleed, and the Wrap Assassin does about 20-25 damage, plus 40 in bleed, meaning if you just land both bleed hits, that's at least 150 damage. If you also land a FaN shot, that's over 250 damage, and if you can land that last hit, you can absolutely take out a Heavy.
