I'm always kind of disappointed when an author describes an elf as 'crazy' and it turns out to be the same old 'lost their mind from living too long' trope. It's a lazy shortcut. The good stuff, the stuff that actually feels unhinged, comes from the intersection of their inherent nature with something that violently contradicts it. An elf who has spent millennia cultivating perfect harmony with a forest going utterly berserk because a logging consortium powered by necromantic engines shows up? That's a specific, understandable madness. Their rage isn't just madness; it's the logical endpoint of their worldview shattered. It becomes a force of nature, but a twisted one. Their grace turns predatory, their long-life perspective allows them to plan revenge over centuries in meticulous, horrifying detail. The 'crazy' part isn't forgetting who they are; it's remembering all too well, and having that memory curdle into something monstrous.
You see it in how they weaponize their own aesthetics. A sane elf's song might heal or grow trees. A crazy one? The melody gets stuck in your head and the trees start growing through your floorboards, slowly, over weeks. Their beauty becomes unnerving, a polished mask over absolute chaos. I think the key is that their insanity should feel elfin. It's not a human madness; it's an immortality sickness, a detachment from mortal concerns so complete that our lives are like mayflies to them, amusing to watch burn. Their key traits aren't just 'hears voices' or 'is violent,' but a sublime, eerie wrongness applied to everything we associate with elves: perfectionism turned to obsession, patience turned to endless, silent stalking, and a connection to nature that becomes parasitic or vengeful.