Alternate

Flawed Impersonators: Alternates can use their action to polymorph into a Small or Medium humanoid it has seen. These polymorphs are not perfect however usually a body part is disfigured or their voice is not quite right compared to their prey. They may also return to their original form. If an Alternate kills its prey, it completes its polymorph, takes memories from its prey. Its statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Nightstalker: Alternates are extremely proficient at hiding in darkness, they get a +10 bonus to stealth checks in darkness. While moving through darkness, they do not make any sound unless they want to be heard by their prey. If they make a Slam attack while in darkness or while they are tormenting their target, they deal an additional 20 damage with the attack. If someone attempts to search for an Alternate with dark vision they have disadvantage on the check.

Death Compulsion: Alternates are extremely proficient in tormenting their prey to make them want to commit suicide so they can assume their form. They will follow their prey around whether it is while they are in town or in their house, turning into deceased relatives or pets that they have had and sounding like them to confuse their prey, they will trap them in rooms asking to be let in for days and days on end, until they finally break and cause them to go insane. If an Alternate torments a target for two consecutive days, they force the target to make a DC:24 Wisdom saving throw or they will begin to find any way possible to end their own life. If they succeed the saving throw the Alternate must continue to torment the target for one more day before they can force them to make another saving throw.

Psychotic Ramblings: Alternates can use their action to attempt to confuse and fear their opponents by speaking various promises or talking like the person they are mimicking. They cause their target to make a DC:17 Wisdom saving throw or be feared. They can attempt the saving throw once again at the start of their turn. If they fail the saving throw 3 times, they are permanently feared against this Alternate and permanently have disadvantage against Psychotic Ramblings from other Alternates.

Multiattack. The doppelganger makes two melee attacks.

Slam. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) bludgeoning damage.