From Blaseball Wiki
The Duendes are a species who superficially resemble humans, but who possess at least one of several peculiar features, including:
- Limited or conditional adherence to the laws of cause and effect
- The ability to selectively erase their own memories
- Generally being considered "real good guys"
- Eyes that peer deep into your soul
- Certain physical characteristics that cannot be described by observers
- The surname "Duende"
- Long, flowing hair.
It is unclear if Duende status is hereditary or acquired through other means.