My Rats are the Best rats

 

Rats are a bit limited in games to those small dog-size rats which is a bit sad

Rats can all sneak, hide, listen and swim, some can track and are very alert
All have blind fighting and night vision 

Were rats are related but not included here except under scenario hooks

Rat Swarm

Natural neutral animal
AC+3 HD 2 Attack swarm Morale 10 Mov 12
Covers 2x1 square causes 2 damage to all in area per round
HP halved cover only one square and inflicts only 1hp
Weapons cause only 1 hp damage, spells or burning torch damage as normal
After battle injured enemies make a vigour save to resist disease -2 all rolls d3 days fever
Swarms mostly defend large nests or starving swarms in sewers or haunted houses

Giant Rat
Giant nuetral animal
AC+3 HDd4 Attack Bite d3 Morale 8 Mov 12
After battle injured enemies make a vigour save to resist disease -2 all rolls d3 days fever
Often live in large nests of 2d6+6 and breed rapidly

Gigantic Rat
Giant nuetral animal
AC+4 HD2 Attack Bite d6 Morale 9 Mov 12
After battle injured enemies make a vigour save to resist disease -2 all rolls d3 days fever
Often live in large nests of 2d4+4 and breed rapidly, these will roam openly attacking people

Colossal Rat
Giant nuetral animal
AC+4 HD4 Attack Bite 2d4 Morale 9 Mov 12
After battle injured enemies make a vigour save to resist disease -2 all rolls d3 days fever

Titanic Rat
Giant nuetral animal
AC+5 HD8 Attack 3 Bite 2d4 Clawx2 d6 Morale 10 Mov 15
After battle injured enemies make a vigour save to resist disease -2 all rolls d3 days fever

Titanic Rat
Giant nuetral animal
AC+8 HD64 Attack 3 Bite 2d12 Clawx2 2d8 Morale 11 Mov 24
After battle injured enemies make a vigour save to resist disease -2 all rolls d3 days fever

Ratlings 
Small nuetral or evil humanoids
AC+4 HD d8/Lv Attack club d4 or dagger d4 or dart d4 Morale 7 Mov 12
3-4 foot or 90-120cm tall rat folk +1/Lv save vs poison and disease

Rat Folk 
Large nuetral or evil abhuman
AC+6 HD d12/Lv Attack spear d8 sword d8 or bow d6 Morale 8 Mov 12
7 foot or 210cm tall ratfolk, leap +1
3HD disease resistance 6HD poison resistance 9HD summon swarm/per day for 1 hour 

Variants
1in4 Rabid Rats save or become infected with disease, hydrophobic, aggressive +2 morale, nauseous and confused.Each week save or lose an attribute point until cured or dead and foam at the mouth
1in4 Horned Rats get a +1 attack action from their horns, d4 horns for local subtype or dominance depending on the strain. Some eventually kill themselves with horns piercing their own skulls and growing into their brains. The skulls of these are salable curios
1in4 Sabretoothed Rats get a +1 damage dice bump from their huge fangs
1in4 Blood Drinker Rats once hit with a bite hang on and keep drinking blood each round until killed. Swarms that do +1pt damage instead. Can reskin these as weasels 

1in6 Plague Rats save or bitten victims erupt in buboes and fever after d4 hours if they fail a save. Halves all attributes, each day save or lose a d4 HP, three saves in a row and they recover but some scarring
1in6 Berserk Rats rats or make shrews instead +2 hit and damage fight to -10 HP, will attack any moving target until non-left, won't attack baby rat while berserk

1in6 Mole Rats Burrow 3 and blind fighting, hairless or replace with actual moles by halving normal Mov speed and increasing Burrow to 6
1in6 Venemous Rats rats a bite from them and a failed save, ten minutes later red and swollen and in pain damage as a bite attack -2 all dice rolls and Mov until healed. With a save just 1hp damage and a bit itchy

1in6 Fast Rats more shrew-like, less less long but +2 Morale and they can hast for a d4 rounds at the start of a fight they are so savage and breed quickly before burning out

1in8 Mutant Rats minor mutation every HD major mutation every three HD
1in8 Swarm Mind Rats the colony are in communication by colonial mind link or aided by a spirit that helps them communicate

1in8 Monkey Rats with a prehensile tail, hands that use basic tools, malicious intellect, leap 3m
1in10 Swarm Form Rats  when killed breaks into a swarm of rats. With a rat swarm to start it breaks into two 1HD damaged swarms covering one 3m circle

1in10 Uncanny Cunning Rats and knack for alchemy, gunpowder and incendiaries. Use traps and biological warfare with pollutants, infected goods and wasp nests

1in10  Chaos Rats regenerate 1hp per round unless from fire or acid

1in12 Zombie Rats +1 HD and undead resistances 12 Morale half Mov
1in12 Devil Rats +1 or silver or fire to harm, Have human-like faces and Chant diabolically and perform dances forming evil sigils. Taunt people through walls and 
1in12 Magi Rats know one level of spell per HD, under 1HD know a cantrip. Intelligent and know one type of spell casters magic they select spells from. Some say they were once a system wizards used instead of books in prehistory that got loose
1in20 Vabour Rats +1 magic to hit, can assume gaseous form a will
1in20 Phantom Rats are spectral non-material rats that can run through walls and/or turn invisible. When they appear visible or through a wall, creatures with lower HD save vs fear for one found 
1in20 Spirit Rats ghostly rats can become invisible, or phase through the ethereal plane to escape peril or reach food. Manifest ectoplasm bodies once per day and these gelatinous slime bodies require magic or silver or cold iron to harm. Once physical they seek food they can gorge themselves on

d12 Rat Adventures
1 Rats in the basements all over the village find and destroy the nest

2 People report a strange minstrel charging money to keep rats from homes and those who don't pay find rat problems increase vastly 

3 Giant rats dragged an orphan into a sewer and the other urchins are in tears and afraid

4 A creepy man has been seen at night and when confronted they saw rats swarm from his coat as he fled

5 A dreadful rat cult has infiltrated a community and rat swarms are becoming more common and bolder in attacking people. Find the cult and stop them

6 A local bandit escaped prison with help from rats and somehow caught them

7 A new crime guild is making territorial gains. Other crooks say the new gang know everything in town and several rival monsters were found dead and rat gnawn

8 Small rat-like people of some kind have been seen lurking about but that has become less important than the recent plague outbreak. The law searching for plague houses and recruiting grave diggers and corpse gatherers

9 Gongfarmers working the sewers are missing and huge chaos rat monstrosities have been seen and heard chanting

10 The town hung a were rat and it was more difficult than planned resulting in the crowd being attacked by swarms and many bitten. The mayor fears reprisals from the rat cult and wants guards for a few days

11 A mad prophet has been screaming and ranting about the menace "Grey Digbert" a rat bigger than a mountain. Nobody was worried until the mad prophet was eaten by giant fleas in his cottage

12 Graphitti dedicated to a demon rat god has been marked around local buildings and locals are having a meeting to do something before it is too late

This is my standard monster format now id like to work through all the basics and classics.