Scarecrows are a sub-race of Undying that have altered themselves even further and integrated non-organic augmentations into themselves.
Most Scarecrows live on the fringes of society and are viewed as monsters by many children.
These humanoids are typically tougher than normal humans.
D&D 5e
The undying and scarecrows are purely cosmetic alterations to humans for game purposes. Variant Human: Must choose Constitution for an Attribute score and choose from Tough or Resilient Feat at 1st level.