Yaga Goo

Amorphous. The goo can move through a space as narrow as 1 inch wide without squeezing.

Deadly to Fey. The goo has advantage on attack rolls against fey and any creature with the Fey Ancestry trait.

Spider Climb. The goo can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Multiattack. The Yaga goo makes two pseudopod attacks. When its Foul Transit is available, it can use Foul Transit in place of one pseudopod attack.

Pseudopod. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) bludgeoning damage plus 3 (1d6) necrotic damage.

Foul Transit (Recharge 4-6). The goo teleports to an unoccupied space it can see within 50 feet, leaving behind a wretched puddle in the space it previously occupied. A creature within 5 feet of the space the goo left must succeed on a DC 16 Constitution saving throw or take 10 (3d6) necrotic damage and become poisoned until the end of its next turn. The first time a creature enters the puddle's space or if a creature starts its turn in the puddle's space it takes 10 (3d6) necrotic damage and is poisoned. The puddle lasts for 1 minute or until the goo that created it is killed.

Puddle Splash. When a creature the Yaga goo can see targets it with a melee attack while within 5 feet of the goo, the goo can teleport to a puddle created by its Foul Transit, if that puddle's space is unoccupied, negating the damage from the attack. If it does, the attacker must succeed on a DC 16 Constitution saving throw or take 10 (3d6) necrotic damage and become poisoned until the end of its next turn.