Don't think it's ever been mentioned in any of her lore, anyone got any idea what it actually is? If not i'll just continue assuming Nidalee is a Vision-esque android with the Time Stone in her head.
It’s the time stone duh
Most likely a random detail put in to make her seem interesting without any reason for it to be there.
It's called an accessoire. Nidalee thinks it's pretty, so she wears it.
It's the Cosmic Gemerald
It's what lets her become animal
When she was adopted by animal, they saw great potential in her so the elder of the clan bestowed the Cosmic Gemerald onto Nidalee so she could be their champion
