AMOEBOID

 These giant amoeboid creatures look like nothing more than puddles of slime, but they both live and move, feeding on metal or wood as well as the occasional dungeon explorer to supplement their diet. But we were not on a station platform. We were on the track ahead as the nightmare, plastic column of fetid black iridescence oozed tightly onward through its fifteen-foot sinus, gathering unholy speed and driving before it a spiral, re-thickening cloud of the pallid abyss vapor. It was a terrible, indescribable thing vaster than any subway train-- a shapeless congeries of protoplasmic bubbles, faintly self-luminous, and with myriads of temporary eyes forming and unforming as pustules of greenish light all over the tunnel-filling front that bore down upon us, crushing the frantic penguins and slithering over the glistening floor that it and its kind had swept so evilly free of all litter.

At the Mountains of Madness, by H.P. Lovecraft

Name: acid blob
Difficulty: 2
Base level: 1
Base experience: 9
Speed: 3
Base AC: 8
Base MR: 0
Alignment: 0
Frequency: Quite rare
Genocidable: Yes
ATTACK:
    Passive only
Weight: 30
Nutritional value: 10
Size: tiny
Resistances: sleep, poison, acid, petrification
Resistances conveyed by eating: None

An acid blob can flow under doors. Due to its unusual body chemistry, It has no need to breathe. It has no eyes, and is therefore impervious to gaze and blindness attacks. It has no mind, and is therefore not detectable via telepathy. An acid blob has no limbs and no head. It is acidic if eaten.

Name: black pudding
Difficulty: 12
Base level: 10
Base experience: 221
Speed: 6
Base AC: 6
Base MR: 0
Alignment: 0
Frequency: Very rare
Genocidable: Yes
ATTACK:
    Bite: Corrodes some armour
Weight: 900
Nutritional value: 250
Size: large
Resistances: cold, electricity, poison, acid, petrification
Resistances conveyed by eating: cold, electricity, poison

A black pudding can flow under doors. Due to its unusual body chemistry, It has no need to breathe. It has no eyes, and is therefore impervious to gaze and blindness attacks. It has no mind, and is therefore not detectable via telepathy. A black pudding has no limbs and no head. It is acidic if eaten. It is an omnivore.

Name: brown pudding
Difficulty: 6
Base level: 5
Base experience: 56
Speed: 3
Base AC: 8
Base MR: 0
Alignment: 0
Frequency: Very rare
Genocidable: Yes
ATTACK:
    Decays for 0d0
Weight: 500
Nutritional value: 250
Size: medium
Resistances: cold, electricity, poison, acid, petrification
Resistances conveyed by eating: cold, electricity, poison

A brown pudding can flow under doors. Due to its unusual body chemistry, It has no need to breathe. It has no eyes, and is therefore impervious to gaze and blindness attacks. It has no mind, and is therefore not detectable via telepathy. A brown pudding has no limbs and no head. It is acidic if eaten. It is an omnivore.

Name: gelatinous cube
Difficulty: 8
Base level: 6
Base experience: 76
Speed: 6
Base AC: 8
Base MR: 0
Alignment: 0
Frequency: Quite rare
Genocidable: Yes
ATTACK:
    Paralyses
Weight: 600
Nutritional value: 150
Size: large
Resistances: fire, cold, sleep, electricity, poison, acid, petrification
Resistances conveyed by eating: fire, cold, sleep, electricity

A gelatinous cube has no eyes, and is therefore impervious to gaze and blindness attacks. It has no mind, and is therefore not detectable via telepathy. It has no limbs and no head. It is acidic if eaten. A gelatinous cube is an omnivore.

Name: gray ooze
Difficulty: 4
Base level: 3
Base experience: 28
Speed: 1
Base AC: 8
Base MR: 0
Alignment: 0
Frequency: Quite rare
Genocidable: Yes
ATTACK:
    Rusts for 2d8
Weight: 500
Nutritional value: 250
Size: medium
Resistances: fire, cold, poison, acid, petrification
Resistances conveyed by eating: fire, cold, poison

A gray ooze can flow under doors. Due to its unusual body chemistry, It has no need to breathe. It has no eyes, and is therefore impervious to gaze and blindness attacks. It has no mind, and is therefore not detectable via telepathy. A gray ooze has no limbs and no head. It is acidic if eaten. It is an omnivore.

Name: green slime
Difficulty: 8
Base level: 6
Base experience: 164
Speed: 6
Base AC: 6
Base MR: 0
Alignment: 0
Frequency: Very rare, only in Gehennom
Genocidable: Yes
ATTACK:
    Touch: Turns you into green slime
Weight: 400
Nutritional value: 150
Size: large
Resistances: cold, electricity, poison, acid, petrification
Resistances conveyed by eating: None

A green slime can flow under doors. Due to its unusual body chemistry, It has no need to breathe. It has no eyes, and is therefore impervious to gaze and blindness attacks. It has no mind, and is therefore not detectable via telepathy. A green slime has no limbs and no head. It is acidic and poisonous if eaten. It is an omnivore.

Name: quivering blob
Difficulty: 6
Base level: 5
Base experience: 59
Speed: 1
Base AC: 8
Base MR: 0
Alignment: 0
Frequency: Quite rare
Genocidable: Yes
ATTACK:
    Touch: 1d8
Weight: 200
Nutritional value: 100
Size: small
Resistances: sleep, poison
Resistances conveyed by eating: poison

A quivering blob has no eyes, and is therefore impervious to gaze and blindness attacks. It has no mind, and is therefore not detectable via telepathy. It has no limbs and no head.