Superclot

Blood platelets evolve to clot far faster, increasing endurance and preventing bleeding from wounds.

Location

Located in the northernmost room of the Abandoned Subway Station in the Subway Tunnels deep below Slagtown. There are no hostile mobs en route (except maybe the odd chobo), so just head down and nab it whenever.

Effects

Superclot's main effect is complete immunity to the bleeding status effect. You will still take bleed damage from weapons and mobs that inflict bleed damage (such as sonic scalpels), but the damage-over-time effect will never apply to you. There's no special message to tell you when it happens. It all works behind the scenes -- you'll just never, ever bleed.

Superclot also reduces the chance that you're successfully fed from by a Vampire. There is a chance for each feed to succeed, but it's rather low, so if you're attempting to feed a friendly vamp they may have to try several times before the feed succeeds. If it succeeds, the vampire will be nourished as usual and you'll take damage, but no bleed effect. If it fails, a message will mention the wound clotting too fast for the vamp to feed, and no damage/nourishment will occur.

Advantages

Cannot bleed. That's it. In theory this should be a good mutation for tanky types, but in practice it's more of a convenience mutation. It's good for Carebear players, since Bleeder is used more often in PvP than PvE, though you may still miss Bleeder's buffs for big-game PvE like soloing bosses.

Also nice for the odd Hideous Freak or Vampire build that will either never rend (Carebear) or doesn't benefit greatly from frenzy. Freaks burn themselves when they bleed and vamps get hungry really fast, so it's convenient to just sidestep all of that.

Disadvantages

Incompatible with the Bleeder mutation, which means no frenzy-on-command. Frenzy is really strong for many builds, giving +2 dodge, +4 brawn and excellent feint resistance. Also, while not being able to bleed is nice, Bleeder's constant passive destress is also very convenient in a different way. (Pedants will tell you that you can frenzy with berserker hypos and human hearts, but in truth it's really hard to match Bleeder's easy consistency outside of Hideous Freak's scare.)

Bleeding wounds are also easy to deal with using suture kits (or improvised bandages if you're dumb). PvP fights usually end too quickly for the bleed over time to matter. If you do get hit with a big PvE bleed from a basilisk powerattack or similar, the damage output of tough mobs is so high that they'll usually stun and then finish you off before you can patch yourself up anyway, and if you're fighting lesser mobs that inflict bleed, then you're likely in no hurry and you might as well suture.

Between these problems, Superclot is often regarded as a waste of a slot. Better to spend the slot on a mutation that actually constitutes a worthwhile buff to your build.