Inverted Monsters

A simple concept. Sum up some classic D&D monsters in three bullet points, invert those points, then make them into their own monster.

As always, if your idea can't be summed up in three bullet points then maybe it's too complicated for an RPG monster.

Art from artbreeder.

Beholder

• Lots of eyes
• Floats and shoots beams
• Hates everything

Becomes

• Eyeless and Blind
• Grounded melee fighter
• Loves everything

Adorer (Inverse Beholder)
STR 15, 8hp, Stony Body (Armour 2), d8 Trample.

• Sniffs out signs of life and is drawn towards them. Has infinite love for all other beings, so much so that it can hardly contain its overlapping emotions.
• If it encounters any beings in conflict for any reason it lashes out as a punishment, hoping it will stop the conflict.
• If it in inadvertently kills another being it does everything in its power to isolate itself permanently.

Rust Monster

• Mostly harmless critter
• Eats metal
• Dumb scavenger

Becomes

• Physically dangerous
• Produces metal
• Ultra smart predator

Steel Demon (Inverse Rust Monster)
DEX 18, 9hp. Two d6 Claws.

• Senses any movement of metal objects within a mile.
• Spits out a hail of metal discs (d6 blast) or a single spike (d10, target pinned in place on Critical Damage). 
• Harasses prey with hit and run tactics from vantage points.

Gelatinous Cube

• Absorbs and dissolves anything
• Weird geometric shape
• Amorphous

Becomes

• Can create anything
• Pleasing natural shape
• Rock solid form

Calciferous Mound (Inverse Gelatinous Cube)
STR 15, Armour 3, Immobile. 

• Hums a hauntingly beautiful song to attract visitors. 
• Can create any stony handheld-sized object from its shadowy innards, but only if it is fed something it wants.
• It longs for knowledge, the more secretive the better.

Purple Worm

• Huge creature
• Burrows around
• Poison sting

Becomes

• Small creature
• Flies
• Healing Touch

Viridian Moth (Inverse Purple Worm)
STR 1, 4hp.

• Begins as a bright green, stinking grub with acidic spit that will eat away at practically anything. This lasts for three days and it is insatiable. 
• When it enters its cocoon form it emits an unpleasant, ultra high-pitched whistle every few minutes. This lasts for one day. 
• When it emerges as a beautiful green moth it can shed spores that heal any ailments and can even regrow limbs with enough exposure. It remembers everything about how it was treated in its earlier phases, and only helps those that have previously helped it. 

Bulette

• A shark, but in land 
• Armoured shell
• Eats people

Becomes

• A bull, but in water
• Soft body
• Delicious to eat

Sharling (Inverse Bulette)
STR 16, 5hp, Big Soft Body (Armour 1), d10 Gore. 

• Patrols its territorial waters and rushes anybody that it sees as a threat. 
• If you can catch one its fatty meat is a delicacy (£2k for a full carcass).
• Anybody that eats some of its meat is Deprived each day they do not eat some more. The addiction wears off after a week of not eating any meat at all. 

Mind Flayer

• Ultra smart psychic
• Eats brains
• Physically weak

Becomes

• Stupid and devoid of empathy
• Absorbs muscle
• Physically strong

Force Leech (Inverse Mind Flayer)

5hp. d8 Sledgehammer.

• Wants to assert physical strength over others and has no concept of empathy
• When it causes STR damage it gains that many "Muscle Points" (MP)
• Can spend MP in place of HP or to add to Damage rolls, to the maximum of their die type