Berserkers

HD 1  AC 11  Oversized Weapon 1d8

Speed as human  Morale 12  Immune Fear, pain

Diehard.  After being dropped to 0 HP, there is a 50% chance that this creature continues to fight for another round before dropping dead.

Types of Berserkers

1. Insane.  A overdose of talakeshi jelly, or the product of too many exotic neurotoxins spread across too few nerves.  Twitches, hallucinations.  Ragged clothing, stained red from self-harm.  Bare feet leave bloody footprints wherever they go.  Attack with hammers, straight razors.  Shouts: "I wanna eat your babies!" "Show me a bucket, and I'll show you a bucket!"  "They bounce if you throw them hard enough!"  "I'm sorry!  I'm so sorry!  You'll forgive me, won't you?"  "Harold!  Harold, how have you been?  How about those twenty silver you owe me?"
2. Ensorcelled.  Supernaturally beguiled into becoming the soldiers for some enchanter.  Their veins glow red under their skin, and steam rises from their panting mouths.  They scream the name of their enchanter when they spot an enemy, when they attack, and when they die.  These are the only three things they'll ever do, and so the name is the only word they'll ever need.  Attack with glittering swords, or a single fingernail, glowing and impossibly long.
3. Viking.  They're here for gold, a specific magical item, or simple to make a name for themselves.  Often it'll be a group of teenagers, striving to kill a noteworthy opponent or die trying.  They'll froth at the mouth and bite their axe hilts.  In the battle-rage they scream like animals, and forget the use of speech.  (They're quite reasonable the rest of the time.)  They wear braided bracelets of their spouse's hair (or their mother's if they are unwed).  Attack with greataxes and greatswords.
4. Deathsworn.  Shorn heads, plastered with chalk dust.  Prayer beads shackled to their wrists.  Penitent's robes.  In exchange for the forgiveness of their sins, these men and women have received their third baptism from the Church--the baptism for the redemption of the damned.  This is effectively a geas spell, with one goal: to seek the greatest sources of destroy them without hesitation or forethought.  (They usually die pretty quickly.)  You'll often find themselves in the darkest corners of the world.  In these places, they attack everyone they see, reasoning that no decent person would ever stumble into such a hellhole.  Attack with huge hammers and spiked staves.
5. Laughing.  Servants of the pain god.  Beneath their black leather armor is an elaborate filigree of scars.  Bottles on their waist are filled with blood, which they drink to slake their thirst.  Around each one's neck is a trussed-up vampire bat, whose saliva they use as an anticoagulant (so their blood doesn't curdle).  They delight in causing pain, but not in prolonging death.  They grin when they are struck, and always die laughing.  They fight with spiked chains and razor glaives.
6. Otherworldly.  It's easy to be careless with your body when you know its only a rental.  Blue skin pebbled with yellow bumps.  Beneath a bandana is a third, empty eye socket.  Wear rags covered in yellow dust.  Speak no known language.  Attack slowly, carelessly.  They fight with glass spears, like elongated icicles.

Berserker Encounters

1. Dungeon Chase.  4d6 berserkers appear, yelling and gnashing their teeth.  They are numerous enough that fighting them is ill-advised.  They intend to chase the party out of the dungeon, killing only the one member who is slowest.
2. Rorshach Test.  2d6 berserkers are attacking some disgusting but benign creature (or creatures), made dangerous by its injuries.  They will urge you to join them in attacking it.
3. Awakening.  2d6 berserkers have located a magic spear (+3 vs angels) and learned the location of a graveyard spirit.  They're going to go wake it up and kill it.  Left to their own devices, they will succeed at the first have of this goal before being killed by the graveyard spirit and the spear trampled into fragments.  This will replace the berserkers on the random encounter table with the much more dangerous graveyard spirit.
4. Trophy-takers.  2d6 berserkers have killed another entry on this (dungeon's/hex crawl's) random encounter table.  Roll again to find out which one.  They appear covered in trophies from their last fight and have 1 special piece of equipment relevant to the thing they just fought.
5. Enemy of My Enemy.  Roll another random encounter and begin that one as normal, preferably with a monster or enemy that would normally go straight to combat.  After 1-2 rounds of this combat, 4d6 berserkers bust into the room and begin screaming how they are going to kill everyone and wear their guts.  This would be a good time to ally with your former enemy.
6. Berserk Animal.  They are accompanied by a big-pissed off animal.  A dire wolf or huge boar (HD 4 each) is traditional.  The berserk animal attacks a random person each round.

Wrinkles

(because no encounter exists in a vacuum)

1. Berserkers are accompanied by a bard, who will not fight.  He is here to record their brave deaths.  He can promise you good compensation if he is delivered to a nearby city.
2. Berserkers are loaded up on all sorts of drugs, especially Talakeshi jelly (lets you always win initiative).  This is stolen, and a local drug lord will want compensation if she hears about it.
3. When you go back to town, you'll hear about the berserkers being lauded as brave heroes who killed lots of monsters.  You'll be expected to join in when honoring their memories.
4. Berserkers were servants of someone else.  They'll expect you to pay compensation for killing them.
5. Berserkers were known and hated.  You'll be rewarded with friendship, connections, and favors.
6. Berserkers were were known and especially feared.  If you can prove that you killed them, you'll be rewarded with 500s.  This will probably involve recovering all of their bodies, which may have been moved by predators or risen as undead by now.