Well you say that - but it depends on the approach and how its executed - so I agree that a green lady telepathically controlling vines like Venom-esque tentacles/extensions of herself I don't think would work.
But what about a Poison Ivy who develops a strain of cordyceps fungi that works on humans?
As the video states some of these fungi flood the brain with powerful hallucinogens and aphrodisiacs to force them to mate with others in order to infect them with the deadly fungus - an even more sinister form of STI caught from what is effectively either a raving dying lunatic who is rotting before their eyes or from an empty eyed zombie whose body is being animated by this sinister fungus....
Some of these fungi infects insects and hijacks their brain and motor functions by first eating through the insects' outer shell and then physically growing through the body of the ant until it enters the brain and takes control - the ant, which at this point is functionally dead, is puppetered by the fungus to find a spot with the right humidity and height in and then forcibly grow through the head and body of its host - permanently killing them and releasing their spores from the highest point to infect as many others as possible.......in fact it will force its unwilling vessel to do this even when the fungus has caused the body to recieve enormous damage, its not uncommon to see ants, cicadas or other insects infected by these type of fungi missing limbs, having gaping holes in their abdominal cavities of even missing entire halves of their body still being forced to move by the fungi controlling their corpse.
Now - this is something that exists in real life and yet is so horrifying that it borders on the uncanny - it also deals with a lot of Ivy's tropes, killer plants, mind control, hallucinations, aphrodisiacs, body horror (SO MUCH BODY HORROR), the triumph of the plant-life over animal life etc.
So if the science of it is grounded - though terrifying and uncanny to the point of feeling preternatural....
all that is needed then is to set the tone and emphasise the horror....
So imagine - the movie opens with a date - at the table is a stunning woman, hair red like fire, a dark stunning green silk dress on, a red smile that doesn't touch cold assessing eyes... we never see her face in full, only these snapshots of a person... across from her is a man of wealth who doesn't particularly care what measures are abandoned so long as it suits the bottom line... despite himself he is nervous for this date... something about this woman was captivating from the start... not like anyone else he has ever met... she wasn't impressed by his wealth or power, she spoke with such passion and steel... he was surprised but delighted when she asked him out to a nice new vegetarian restaurant he thinks it goes well enough, but she leaves before dessert and never even bothers to come up with an excuse, the man leaves dejected but otherwise fine - several days pass and the man isn't well at all, he has been sweating, sick, shaking and now he is hallucinating, horrifying visions that melt the world before his eyes, unanchor his sense of times as seconds stretch into eternity and days wheel by between the torturous effort to force one thought to follow another... more days pass he becomes irrational and... to his confused horror... unbearably aroused - he tries to suppress it... he leaves his expensive apartment building.... he feels suffocated in their and needs to restock on new medical supplies, there are now strange rashes on his torso and he feels like there is something wrong..... he walks past several women on the street, he avoids looking at them as now the sight hurts, his body rattling with need.... he leaves himself and when he returns to consciousness he realises he is in the middle of trying to force himself on a woman, they are pleading and screaming at him - in horror at what he almost did and terrified of whats happened to him he flees and locks himself in his home - he is too afraid to go to the doctor or to work or to leave at all in case the person he assaulted has filed a report with the police - as the days pass and the phone rings with people wondering where he is, why he hasn't been to work in over a week, he becomes more and more paranoid, sees ever more horrifying visions, he tears the phone from the wall as the noise of it screams as it, he closes all curtains and blinds as the daylight burns his red and weeping eyes.... but in time he begins to forget everything else as his body begins rotting before his eyes, parts of his hands, feet and even skin begin to drop off, liquify and slide from the meat of him as these strange things begin to grow through him, the pain and the drugs in his system make him animalistic, driving him insane he claws at his own flesh with the hope of getting it out - reaching blood or even bone - but beneath his skin is more of the thing growing inside him, forming mushrooms, blooming in strange colours and shapes, alien to the body of any animal... eventually his body stops hurting... but he also stops thinking... he just knows he needs to get high, as high up as he can get... he runs... people stop or scream as he runs past them on the streets, others vomit at the sight of him or stare in shock, some even look about expecting film crews as though they have wandered onto a movie set.... he sees none of this, he sees nothing at all and all he does is feel the need to get to the top of the place resonating in his brain... the image of a place once familiar in his mind that now is all thats left of the man whose twisted broken body is being forced to run past the horrified faces of people he once knew but no longer recognized, past the doors of collegues who are now part of a dream he no longer remembers... he climbs and climbs until at last he opens a door and sees nothing but blue sky and feels relief... his shambling body forces him to the ledge and below him looking far, far above to the pinnacle of this tower that once was this man's empire, his life's work are the terror-struck faces of the crowd below arriving in time to start the work day only to face an image that will be part of their waking nightmares to the day they die......
But the man doesn't seen this - or anything anymore - as the long tendrils of the fungus have at last grown through the soft flesh of his weeping eyes crawling upwards and joined by their brothers that even now force themselves through the rotting matter of what was once the dead man's brain, skull, flesh and hair to reach upwards towards the rising sun........
Later on, its dark, the police have been there all day the scene is surrounded by tape and lights, the officers at the scene as far from the.... body... as they can get away with, they avert their gaze as Gordon looks over them, ashamed to be so afraid to do their own jobs, to be judged by Gordon's stare... but far more afraid to go near the thing near the ledge, some glance upwards to a light in the dark clouds above showing a symbol..... out of the shadows steps a dark figure, made darker for the contrast of the harsh lights illuminating the scene - Batman steps past the threshold of terrified detectives across the unseen barrier they hope to protect them from the sight before him now, some visibly relax as they see the Dark Knight venture forth where they would otherwise tread. Batman steps forward and gazes on what may have once been, and by eye-witness accounts apparently once was, a man - now only recognizable by the vague suggestion of limbs, maybe a mandible bone and few other spilled viscera.... now dominated by the tall and proud mushrooms growing from the decaying soup below it some almost glowingly pale and others of posionous colour.....
The shot focuses on Batman's face, its stoic but there is the suggestion of horror, bewilderment, disgust, anger....
We hear Gordon's voice off screen "....what... what is this... what could have done this."
"I don't know...yet".
Something like this, to me, is horrifying and fantastic, yet does so while still anchoring itself in the Gothic and the possible (no matter how improbable), it plays on the unknown rather than the blatantly magical - there is no way to have ivy as a green woman who magically can control plants telepathically in a way that would gel with the tone of the Reeves universe.... but something like this? I can see it.
