Parasite. While grappling a creature, the body snatcher takes half damage. The other half is dealt to the creature it grapples.

Shapechanger. The body snatcher can use its action to take the form of any creature it has devoured within one month. Its statistics remain the same, except it gains the size, speed, and languages of the chosen creature. If it dies while shapechanged, the body snatcher reverts to its true form.

Fluid Form. The Body Snatcher is capable of grappling up to two creatures of medium size (large creatures count for 2, small for one half). 

Innate Spellcasting. The body snatcher's innate spellcasting ability is Intelligence (spell save DC 13). The Body Snatcher can innately cast the following spells, requiring no material components:

2/day: Mind Spike, Invisibility

Multiattack. The creature makes three attacks with its tentacles or crush action, and attempts to grapple up to two creature (the body snatcher only attempts to grapple as many creatures as it could potentially hold).

Tentacles. Melee Weapon Attack: +6 to hit, reach 10 ft., 1 target. Hit: 10 (2d6 + 3) [bludgeoning] damage. If the Body Snatcher is not already grappling two medium creatures, its target must make a STR or DEX saving through (its choice) of DC 15 or be grappled. While grappled, the creature is unable to breathe and can last a number of rounds up to is CON modifier (minimum of one). A creature can use its action to repeat this save on each of its turns.

Crush. A grappled creature makes a DC 15 STR saving throw. On a failed save it takes 21 (4d8 +3) bludgeoning damage, or half as much on a successful save. 

Infest. If a creature dies within 30 ft. of this creature, it can use its reaction to move to its corpse and possess it. While possessing a corpse, the creature retains its own statistics but takes on the creature's size and speed. If the Body Snatcher is not removed by means of a lesser restoration spell within 24 hours, the body is consumed and destroyed.