Owlmay

Owlmay are a race/class/organization/something from the Dungeons & Dragons setting of Ravenloft, invented by fans to adapt the concept of the Swanmay to their beloved Gothic Horror Dark Fantasy setting.

Introduced in the Book of Shadows for Advanced Dungeons & Dragons 2nd edition, the owlmay is almost literally described as the Demiplane of Dread analogue to the swanmay; mechanically handled as a monster, they are a secret order of human and Half-Elf women (mostly rangers, but about 10% are druids of the "caretaker" variant) dedicated to the protection of nature. To pursue this goal, they use an enchanted feathered token or undergarment that allows them to shapeshift into the form of a giant owl, as well as rendering them immune to non-magical damage. Like their swanmay counterparts, stealing this item traps the owlmay in whatever form it's currently in, but also has some extra nastiness, because this is the original grimdark D&D setting. If their feather token is stolen, the owlmay is compelled to remain within 1 mile of it at all times, but cannot hurt the current bearer. If it's destroyed, the owlmay is trapped within a 1-mile radius of whre it was destroyed, but will also inexorably go mad, unless an owlmay of at least 2 levels superior crafts them a new token.

Owlmays seek to protect the wilderness from anything they consider threats, which can include humanoids, but their primary enemy is the undead. Weirdly, they tend to ignore therianthropes.

You can actually play an owlmay in 2e, where, like the swanmay, it's treated as a race. Start with Human or Half-Elf, but racial ability score adjustments are +1 Dexterity, +1 Wisdom and -1 Strength instead of the normal effects, and also they have racial class and level restrictions; Ranger 14, or Druid (Caretaker) 12. Then just add the mechanics for using the feather token and its transformative powers.

They were updated to Dungeons & Dragons 3rd Edition in the Undead Sea Scrolls 2002. As this predated the conversion of the swanmay, the 3e owlmay is treated as a monster template rather than a prestige class.