The following mainly comes from initial traditional tribes in general, not including tribes who have mixed origins and other case-by-case variable exceptions.
As one of the nine foundational tribes, the [Tall treeman Tribe] were initially as forest tribe who had deep tradition on tree-worshipping. After receiving their own Grimm-form,
[Grimm-form appearance]
black vertical tree-bark-like strips tattoos on face
purple skin
[Grimm-form ability]
Combat Application:
[Societal Aspects]
[Cultural Aspects]