Critters is a random monster generator for Microlite20 which generates a random name and set of stats. What the creature looks like, what it's weapon or natural attacks are and how it behaves is entirely up to you - consider it an inspiration tool for those times when you want something not in any Monster Manual or the SRD.
It is also available for download as a stand-alone Perl application. See this post on the ENWorld thread for usage instructions.
The following critters were randomly generated then fleshed out by rycanada, GreyWulf and Pilsnerquest:
veiper
HD3 (24hp), AC16, By weapon +5 (1d6+5)
The veiper is a small, fast snake-like humanoid which attacks with a curved shortsword while tasting the air in their tongues.
wacker
HD1 (6hp), AC11, By weapon +1 (1d12+3)
Wackers are ogre children trained to raise the alarm if non-ogres approach their cave. They carry a drum and a huge hammer which is devastating in combat.
inchube
HD3 (14hp), AC14, Natural +6 (1d8-3)
Inchube (pronounced inc'hoo'bey) are water spirits found in fast flowing icy streams. They dance along the snow at the edge of the stream to lure travellers to their deaths.
quoy
HD2 (11hp), AC14, Natural +2 (2d4+4)
The quoy is an animated cypress tree that launches splinters at its foes
teiyable
HD5 (38hp), AC16, By weapon +8 (2d2-2)
The teyable is a cousin of the shambling mound that controls brambles and weeds to constrict its opponents
huthe
HD4 (23hp), AC17, By weapon +7 (1d10+3)
Huthe are a swarm of wasps that take a vaguely humanoid shape. Their origins are a mystery, but they tend to attack those who carry precious gems most violently.
dubation
HD1 (5hp), AC15, By weapon +3 (2d8+3)
Dubations are water-loving sparrowlike creatures that can be identified by their bewhiskered facial plumage. They are much tougher and more territorial than normal sparrows, however, and interact like a pack of wolves when dealing with threats.
laniss
HD4 (28hp), AC14, By weapon +4 (2d10-2)
Laniss are giant harvester spiders, and are largely docile creatures often harnessed as mounts by goblins.
unove
HD4 (24hp), AC15, Natural +6 (1d12+3)
Unoves are bone-white, spine-covered drakes with a pair of neck frills that join to one in the centre of the back.
vedition
HD3 (18hp), AC15, Natural +3 (2d6-4)
Veditions are a race of poisonous, blotchy humanoids that dwell in city sewers. They attack with their long fingernail-like claws, which naturally secrete their poison.
jiet
HD1 (4hp), AC15, Natural +2 (2d2-2)
Jiet are spirits who haunt a person's dreams for three straight nights. If the person fails MIND checks, DC 15, for each of the three consecutive nights the spirit assumes a physical body drawing half the persons stats to its new body. The person, who can sense the spirit, must hunt it down and destroy it to make their body whole again.
gow
HD2 (9hp), AC12, Natural +3 (2d6+3)
Gows are seemingly harmless looking livestock oddly found out in remote regions. However, these animals are dangerous and will slowly close in on unsuspecting persons while releasing a soundless and incapacitating gas that renders a person nauseated, DC 8 +1 for each additional Gow. The livestock will then attempt to eat the person. It is rumored that a tipped Gow cannot release the noxious gas.
brir
HD3 (18hp), AC16, Natural +6 (1d10-2)
Brir are fat humanoids who will attempt to grapple a person as their attack. On the next round, if still able to hold the grapple, they will seemingly deflate themselves revealing a gaunt body that protrudes long thin quills (Natural +6 (1d10-2)). They will use this natural quill attack until the person is dead or the grapple is broken at which time the Brir's body will bloat again disguising the quills.
maxiff
HD10 (84hp), AC23, Natural +12 (2d6+5)
A very, very large mastiff. Very large. It's head is three times the size of yours, and it's jaw could rest on your head while standing. Bred by giants as guard dogs, but sometimes found in the wild where pools of their saliva are sometimes mistaken for large puddles. Their breath smells awful.
tepeing
HD1 (7hp), AC11, By weapon +3 (1d10+2)
A thin organge skinned humanoid barbarian race from the outer planes. They wield greatswords and wear still-living furs of some unknown creature that growl and snap at foes in combat.
thozzive
HD8 (52hp), AC22, Natural +9 (2d4+4)
Thozzives are the equivalent of giant snails from the elemental plane of Earth. They move slowly though soil leaving only their slime in passing. This eventually becomes veins of silver lacing the rock. Dwarves have been known to breed thozzives to re-seed silver mines with some success. They attack rarely, by sliding over their opponents with their rock-encrusted bodies.
lownment
HD1 (6hp), AC12, By weapon +1 (1d4+5)
A living lawn ornament. They look much like pottery garden gnomes and attack with their little fishing rods and garden implements. They are constructs originally given life by now forgotten magic, and multiply by an unknown method on nights when the sky is clear. A single lownment can become hundreds in a matter of days. Lownments are hated by real Gnomes who try to smash them into little pieces on sight.
By Kensatana, from the ENWorld thread
FROZEN
Rabid Ice Bear
3d8+6 (19hp), AC 11, claws +5 (2d4+4)
Once it hits, apply 2d4+4 crushing damage automatically. Blot-shot eyes, and tons of saliva. Something's wrong with this bear! Anybody bitten by the bear save phys+STR vs. DC15 after combat or suffer STR-1, MIND-1. Next morning, save phys+STR vs. DC15 again if you failed after combat. If you fail again, suffer STR+2, DEX-1, MIND-3, and blood-shot eyes. Heal as normal ability damage.
Storm Yeti
5d8+10 (33hp), AC 13, slam +8 (1d6+3)
A huge hulking shadow moving in the shadows amidst the raging blizzard. Will you venture forth and investigate? Meet the angry Yeti who resents trespassers. Sub 8 during a snow storm for a surprise slam!
Ice Wolf
1d8+2 (7hp), AC 12, bite +2 (1d4+1)
Ice wolves usually hunt in packs of 15 or more wolves, staying out of range, picking on any stragglers, preventing any decent rest (no healing or recovery from magic drain when surrounded by wolves out on the ice), attacking when the party is weak, such as after a fight with an angry bear.
Frozen Shaman
Undead, 3d8 (13hp), damage resistance: 5/slashing, AC 15, slam +3 (1d4), magic missile every odd round (1d6+3)
Evil shamans are often left behind by the wandering tribes to die in the ice. Some of them cling to their life beyond all reason, however, and thus their dessicated corpses walk the frozen wasteland in the search of warmth & food. It will try to sneak into a camp, release pack animals, and steal as many provisions as possible. Frozen shamans will only fight to save their lives. They're more interested in the food.
Greater Ruaarz
9d8+18 (58hp), damage resistance: 5/fire, AC 17, bite +11 (2d6+4), cold breadth every odd round (2d6+2)
These giant ice snakes can travel hidden below the snow or below the ice (Sub 12) to approach their prey. They'll raise their ugly head up to twice the height of a man to release a minor ice storm from their bellies, and then swoop down to kill the most foolish of their enemies who dared approach them. Once it has killed its first enemy, it will drag him down below the ice or snow and start to retreat. If left alone, the one victim will satiate it for many weeks to come.
TEMPERATE FOREST
Stick Man
2d8 (9hp), damage resistance: 5/fire, axe, AC 16, slam +2 (1d6+4)
These animated stick men look frail and thin, but they are fast, hard as iron wood, and animated by a furious spirit bent on kicking out the intruders. Usually you'll find 6-12 of them defending a particular area. They won't pursue retreating foes unless set on fire using oil or magic, in which case they will die in two rounds anyway.
Oak Golem
7d8+14 (46hp), damage resistance: 5/fire, axe, AC 17, slam +11 (1d10+8)
A gnarled old tree sitting atop some boulders suddenly turns to life. Wood and stone start shifting and form into a very broad roughly humanoid with fists the size of an whole halfling. These golems will not start a fight on their own as they're usually fast asleep unless set ablaze or wakened by other wooden creatures such as stick men. Setting them afire using oil or magic will destroy them in four rounds. In those final rounds, they can tear boulders from their dying bodies and hurl them (3d6+3).
Fox Spirit
2d8 (9hp), AC 15, composite short-bow & arrows +5 (1d6), short sword +2 (1d6)
The fox spirits usually travel in hunting bands of 12-20 at night and are used as scouts by other forest spirits.
Beech Child
1d8 (5hp), damage resistance: 5/fire, axe, AC 10, slam +1 (1)
As you approach the tree overgrown with moss, you recognize the shape of a naked child leaning against the tree. It's skin is brown and green, as if overgrown with moss itself, and it's eyes have that magenta stare. In fact, the stare will daze all that look at it (save com+MIND vs 15 or be dazed for 1d4 rounds), and the child's touch will slow any that are hit (save phys+MIND vs 20 or be slowed for 1d4+3 rounds). These children of the woods are usually seen on their own, with 4-12 fox spirits hiding in waiting to shoot down anybody who trespasses.
Wicker King
10d8 (45hp), damage resistance: 5/fire, axe, AC 15, greatsword +14/+9/+4 (1d10+8)
Usually found governing an enchanted forest from the darkest grove, the horned wicker king will only join battle after having summoned all his allies. A typical wicker king will have two or three oak golems and up to fifty stick men to fight for him.
