Order of the Doppelganger

Your blood has been mixed with that of other-worldy abberations to better augment your shape-changing ablilities. You were designed to hunt down monsters with the full array of humanoid abilities, from the wings of the Aaracokra to the claws of the Leonin.

Restriction: Changelings Only

Only changelings can follow the Order of the Doppelganger. The infusion of abberant bloods and training there after requires the subject to be innately able to shape-change.

Abberant Blood

Your blood has been infused with that of abberations, this has changed you enough to give you the monstrosity creature type. Any spell or ability that targets monstrosities can target you aswell.

Defence Immersion

When you choose this archetype at 3rd level, you gain the ability to take on the defenses and vulnerabilities of races you change into, this includes any resistances, immunities, and vulnerabilities to damage and conditions. In addition, you gain any natural ac or bonus/penalty to ac that the race has. This includes abilities like the Tortle's Shell Defense and the Goliath's Stone Endurance traits aswell.

Sensory Immersion

At 7th level, you gain any additional senses the race you change into has. However, you also receive any penalties to your senses that the race has. This includes abilities like the Kobold's darkvision and sunlight sensitivity, as well as, the Harengon's hare-trigger trait.

Movement Immersion

At 11th level, you gain the ability to change into humanoids that don't share your arrangement/number of limbs, such as, the Aarakocra or the Centaur.

You also gain the base movement speeds and any movement modifiers the race has. Water-breathing/hold breath abilities are gained if you become an applicable race, though if the race has a water dependency you gain it as well. This includes abilities like the Tabaxi's feline agility or the Harengon's rabbit hop traits.

Offense Immersion

At 15th level, you gain any natural attacks gained by the race you change into. In addition, you can apply your crimson rite to your natural weapon's. While it's active, they become magical for the purpose of overcoming resistances or immunities. This includes any abilities like the Minotaur's goring rush and hammering horns, as well as, the Dragonborn's breath weapon.

Total Immersion

At 18th level, you can change into any humanoid from size small to size large and take on all aspects of the race. While shape-changed you adopt all racial features except ability score changes, languages, and tool/weapon proficiencies, you also retain the monstrosity creature type at all times and any innate spellcasting uses your intelligence modifier. This includes all features including special actions, movement speeds, senses, innate spell casting, etc.