(I nicknamed the sibling Oliver because it sounded unisex to me when i wrote this before i looked it up)
Always liked the idea of Jonathan, master of fear, having a sibling who people find more disturbing than him. Like, imagine you're visiting the new neighbor that just moved in to be polite for politeness sake and the thing that opens the door is a 6,5 burn victim with a stare that pierces your soul. And the person you're supposed to be scared of is hunched over (due to chronic pain) on the couch like a scrawny cat. Oliver's unfortunate face to face encounter with an explosion gave them the unexpected upper leg to match Jonathan's scowl, they make fun of him for it as a coping mechanism, he lets them.
I imagine that before the incident Oliver was a rather anxious person that barely left home and who relied heavily on Jon for stability, until, you know. And gained the confidence to turn their life around. Moving out of the states and into a cosy house on the countryside, becoming the official, unofficial cryptid by the locals. Despite their deformities Oliver gained the farmers trust due to their hospitality and willingness to lend a hand. Whenever a stranger shows up to the fields and encounters the town's “cryptid” they've heard so much about the conversation usoly goes like this.
“So, your the cornfields Scarecrow”
“oh please, Scarecrow is my brother, call me Bailey”
Can't decide whether the name Bailey is a nickname the farmers gave Oliver after they didn't give them their name when asked (also because they had a habit of lounging on hay bales). (Also also, i came up with that name because if someone were to call out to them they would say “Hay, Bailey” like hay bale). Or if they changed it and their last name as to not be recognised as having the same last name of a criminal, and thus be targeted. I can imagine Jonathan coming up with that. Otherwise I like the first idea more because it builds more character with the farmers and their relationship with Oliver.
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Anyways, entering the bad timeline where Jonathan was also caught in the explosion, but unlike Oliver, perished, leaving his sibling behind to mend their wounds involuntarily. Remember in the first ask i sent where I wrote “Or, one of them is “normal” but picks up the mantle of Scarecrow once their sibling is killed off”. That, but instead of Oliver being resentful they're mournful but don't know how to deal with it. So, due to their physical and mental scares, and the insertion of Jonathan's garbes, they make their own getup. Stalking Gotham, watching from afar of the ongoings of the everyday man. Their unwillingness to appear in the light have people mistake them for a ghost, and once witnessed one to many times before a disaster struck, is labeled a bad omen.
In reality, Oliver is a person plagued with trauma that didn't get the time to grieve, so they bore his image instead, wearing clothes bigger than them and carrying around a stick to help them with their limp. A noose hung around their neck, a failed attempt at joining their brother, and to top it all off, a deformity that leaves them unrecognisable. All these superstitions rounding the grapevine reaches the caped crusader's ears, and he investigates this “ghost of Gotham”.
OOOOOh I love this! Poor Oliver I just wanna hug them so bad 🥺😭 This is really good, I would love to read more about this kind of headcannon!