Devastation Drive-In — 'Robot Monster' (1953)

Setting Seeds:  Robot Monsterpocalypse

Once The Ancients unlocked the secrets of atomic energy, it was only a matter of time until they discovered the most powerful weapon in the known universe:  the Cosmic Ray!  Intergalactic beings known as the Ro-Mans took notice, however...

...and decided that it was necessary to neutralize the threat posed by homo sapiens...

...BY ANNIHILATING THE ENTIRE HUMAN RACE...AND THEN DESTROYING THE EARTH ITSELF JUST TO BE THOROUGH!!!

An entire Mutant Future setting can be designed around an apocalyptic invasion from space by the Ro-Mans.  The ape-bodied mechanoids hail from the farthest reaches of space, and wield wondrous technologies that seemingly defy all scientific laws and principles:  teleporters, infinite-distance sensors and communicators, planet-eradicating weaponry, and even time machines.

In one potential Mutant Future, the Ro-Mans landed and laid waste to entire cities with their calcinator beams (or C-Rays), which instantaneously caused all of Earth's cities to crumble, and all life forms "above lepidoptera level" within to perish.

The only defense against the effects of the calcinator beam is an innoculation from an extremely rare antibiotic serum that makes the recipients immune to all diseases...and, inadvertantly, to death-rays from space.  So, those given the injections are now the last people on the planet, eking out meager existences in the ruins of civilization...all the while hiding from the Ro-Man hunters sent to exterminate them!

Ro-Man

No. Enc.:  1 (1)
Alignment:  Chaotic
Movement:  60' (20') 
Armor Class:  -2
Hit Dice:  350 hit points
Attacks:  2 or 1 (2 fists, 1 beam)
Damage:  2d10 / 2d10, or special
Save:  L20
Morale:  10
Hoard Class:  XVI, XVII, XIX, XXI, XXII
XP:  20,000

A Ro-Man is a stocky, 7' tall extraterrestrial construct with a gorilla-like body and a helmet-like head.  They have computerized minds and sensors.

Ro-Mans [sic] are powerful physical combatants, pummeling with mighty fists...and if both fists successfully hit in the same round, they can squeeze its target for an additional 2d12 damage.  But their brute strength is almost an afterthought when compared to their godlike powers. 

A Ro-Man can detect and focus on any and all sentient life on a planet, right down to the specific location of any given individual.  It is immune to all attacks and damage from any man-made weapon ("the arms of the entire world tried and failed..."), and all forms of disease, poison, and energy.  And one cannot forget their individual calcinator rays, which burst forth in a 100' radius and kill everything larger than a moth not treated with a special vaccine...with no Saving Throw allowed.  Ro-Mans are immune to the effects of their fellows' C-Rays.

There are only 3 ways to defeat a Ro-Man:  bypass its logic core with philosophical musings and emotional quandaries (in other words, teach it how to be "a hu-man"), entice it with a female Pure Human with a CHA of 13+, or have it be destroyed at the hands of its commanding officer, a being known as a Great Guidance....

Mutations:  Unique Mutation ("Calcinator Beam"), Unique Sense ("Life-Sense")

Ro-Man — Great Guidance

No. Enc.:  1 (1)
Alignment:  Chaotic
Movement:  60' (20')
Armor Class:  -4
Hit Dice:  550 Hit Points
Attacks:  2 or 1 (2 fists, or 1 beam)
Damage:  3d10 / 3d10, or special
Save:  L20
Morale:  11
Hoard Class:  XVI, XVII, XIX, XXI, XXII
XP:  40,000

A Great Guidance is the intergalactic commander of the Ro-Mans.  It possesses all of a typical Ro-Man's abilities and defenses, plus three unique powers.

First, a Great Guidance's C-Ray not only has twice the radius, but it is powerful enough to instantly slay a Ro-Man.

Second, a Great Guidance can unleash Cosmic Tube Rays, which open vortices into the prehistoric past and draws forth 2d10 dinosaurs into the present.  These reptiles berserkly devour every living thing—animal and vegetable—they encounter.

And, lastly, a Great Guidance can bombard a planet with "cyclotronic vibrations" strong enough to "knock [it] out of the universe."  These beams can shatter an Earth-sized planet to dust in only 3d4 rounds.

All of the above powers have no maximum range, and can be broadcast across space, and through communications media (vid-screens, etc.).

Unfortunately, the computers governing the Great Guidances are the most advanced in the cosmos, so appeals to emotion, reason, or philosophy go ignored.  Great Guidances are beings of pure intellect and drive, and never fall prey to human manipulations.

Mutations:  Unique Mutation ("Calcinator Beam"), Unique Mutation ("Cyclotronic Vibrations"), Unique Mutation ("Cosmic Tube Rays"), Unique Sense ("Life-Sense")

Devastation Drive-In — 'Slithis' (1978)

Environmental Hazard:  Slithis

As the nuclear plants of The Ancients fell to disuse and disrepair, they began to leak radioactivity into the sky, the soil, and the water...

...and not only did the water absorb the powerful atomic energies...

...IT BEGAN TO ABSORB EVERY LIVING THING—ANIMAL, VEGETABLE, AND MINERAL—WITH WHICH IT CAME INTO CONTACT!!!

Slithis is a protoplasmic "organic mud" found downstream from Ancient nuclear power plants.  It is both organic and inorganic, and emits slight Class 1 radioactivity.  (Prolonged, long-term exposure, however, causes tumors, deformations, and even death.)

Pools of slithis are passive hazards much like tarpits...but those that fall into their depths not only drown, but are also absorbed and assimilated upon death.  Bacteria, algae, animals, humanoids:  all are incorporated into the slithis...and the slithis then takes on its victims' characteristics!

When a slithis pool has absorbed 25 HD of living things, the goo coalesces into a monstrous, ambulatory, carnivorous...thing.  All manner of mutants can arise from slithis [meaning the Mutant Lord can use it as a default, all-purpose monster maker], but the most typical result is an amphibious humanoid with an overpowering hunger for flesh and blood....

Spawn Of The Slithis

No. Enc.:  1 (1)
Alignment:  Neutral
Movement:  75' (25')
  —Swim:  45' (15')
Armor Class:  3
Hit Dice:  10
Attacks:  2 + special (2 claws)
Damage:  2d6 / 2d6, + special
Save:  L7
Morale:  12
Hoard Class:  None
XP:  3,800

Spawns of the slithis are doughy, lumbering beasts that stalk waterways, sewers, and Ancient ports.  They arise from pools of slithis, but migrate away in search of live prey. 

Spawns of the slithis devour anything they catch, but relish mammalian viscera most of all.  If a spawn of the slithis successfully strikes with both claws in the same round, it savages its victim's abdomen for 2d8+4 damage.  Once tearing into the innards, the creature fixates on feasting (doing only automatic 2d8+4 biting damage each round), and ignores all other incoming attacks.  Only when the prey item is dead will the spawn of the slithis move on to other foes.

The creatures regenerate rapidly when submerged; in fact, the worst way to dispose of a vanquished spawn of the slithis is to dump it back into the waters from whence it came...!

Mutations:  Aberrant Form (Gills and Lungs), Pain Insensitivity [D], Regenerative Capability (Modified)

Devastation Drive-In — 'The Being' (1983)

Contaminoid

No. Enc.:  1 (1)
Alignment:  Chaotic
Movement:  120' (40')
  —Burrow:  30' (10')
     —Ooze:  30' (10')
Armor Class:  2
Hit Dice:  10
Attacks:  3 or 1 (2 claws, 1 bite, or 1 tongue-lash)
Damage:  1d10+4 / 1d10+4 / 1d12+4, or 1d10 + special
Save:  L12
Morale:  11
Hoard Class:  VIII, IX, XIV
XP:  8,700

Centuries after The Ancients themselves had faded into oblivion, the toxic seeds of their downfall still lay dormant deep within the earth...

...UNTIL THEY DAY THEY AWOKE AS RAVENOUS, LIMB-RENDING MONSTROSITIES NO BARRIER COULD CONTAIN!!!

Contaminoids, cyclopean beings with bodies seemingly comprised of butchered meat, are Pure Humans and Mutant Humans thus transformed by prolonged exposure to underground toxic waste and radioactivity.  The change brings about a savage hunger for human flesh...and a wide array of abilities with which to acquire it.

In close quarters, contaminoids are savagely strong and brutal...but they're just as deadly at range, for their forked tongues can shoot out a distance of 30'.  If a contaminoid successfully hits with its tongue-lash, the victim can be dragged in for a free biting attack, or strangled at range for 1d10 automatic damage per round (escaping requires severing the tongue by doing 15+1d6 damage against it).  However, if the creature hits with its tongue with an Attack Roll of 18-20, the target must make a Saving Throw Versus Death.  Success means strangulation as above...but failure indicates immediate decapitation.

Contaminoids retain enough of their intelligence to be cunning hunters (always Surprising on a roll of 1-3 on 1d6, and often isolating victims to pick them off one by one) and masters of infiltration and escape.  Not only can they tunnel beneath the earth, but they can assume a liquid form to ooze through even the smallest cracks and openings.  They are particularly fond of seeping into places where the occupants feel secure, such as locked vehicles or (seemingly) secured rooms, and then reforming for an an attack that Surprises on a roll of 1-4 on 1d6.  In pure liquid form, a contaminoid is immune to all damage from physical attacks, weapons, and explosions, and can only be harmed by energy attacks or Mental Mutations.   They leave a sticky green residue wherever they travel.

The beasts are strictly nocturnal, as direct sunlight disintegrates their skin at a rate of 2d6 damage per round.  They lair in hidden underground ruins and containment facilities, and litter their dens with reminders and tokens from their former lives.  Some contaminoids even visit their former families in the night, without incident...leaving only a slime trail as evidence of their presence.

Mutations:  Aberrant Form (Amorphousness), Aberrant Form (Elongating Tongue), Accumulated Resistance (Pollutants), Frailty (Sunlight-Sensitivity), Night Vision, Reflective Epidermis (Radiation), Regenerative Capability, Vision Impairment (Light Sensitivity) [D]

Devastation Drive-In — 'Sting Of Death' (1966)

Man O' Were

No. Enc.:  1 (1)
Alignment:  Chaotic
Movement:  75' (25')
     —Swim:  75' (25')
Armor Class:  7
Hit Dice:  9
Attacks:  2 (2 claws)
Damage:  1d8 / 1d8, + poison
Save:  L8
Morale:  10
Hoard Class:  XV
XP:  3,100

Ancient scientists seemingly had no scruples or morality, and would explore every avenue of unhinged science...

...and in laboratories hidden deep in the darkest swamps, they combined sea water, electricity, chemicals, and human blood...

...TO CREATE THE ULTIMATE TREACHEROUS, LECHEROUS FUSION OF MAN AND MAN-OF-WAR!!!

A man o' were is a twisted being that infiltrates a swamp- or oceanside community to sow murder and mayhem.  It appears and acts as an ordinary Pure Human, but when stressed, angry, or seeking revenge against perceived slights and/or romantic rivals, it spends 1 full round transforming into a mind-bending half-man, half-jellyfish hybrid.  The creature grows savage claws, dangling tentacles, and a bulbous, inflated head.

Men o' weres are cunning strategists, and often set traps, sabotage vehicles and buildings, and attack from ambush.  Their claws inject Class 17 poison, but the poison is slow-acting, so those struck get 2 separate Saving Throws to avoid death [if failing the first roll, the victim can roll again to Save for half damage].

A man o' were can summon 3d10 common jellyfish to come to its aid during aquatic battles.  The animals each have 1 HD, do 1d4 damage, and inject Class 3 poison.

Mutations:  Aberrant Form (Gills and Lungs), Toxic Weapon ("Death-Sting")