Actions

Multiattack The Body Snatcher makes two Slam attacks.
Slam Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 2d6+3 bludgeoning damage, and the target must succeed at a DC 15 Strength Saving throw or become Grappled (escape DC 15). A creature that is hit with a Slam attack while surprised is automatically grappled. The Body Snatcher can only grapple one creature at a time.
Invade The Body Snatcher's jaw opens into a wide, three pronged maw as it attempts to latch onto the mount of a creature it is grappling. The target must make a Strength (Athletics) or Dexterity (Acrobatics) check, contested by a Strength (Athletics) check made by the Body Snatcher. If the Body Snatcher succeeds, it ejects skin, and moves into the grappled creature: the grappled creature becomes the Body Snatcher. The body snatcher regains all hit points and automatically recharges its Electric Torrent ability. 
Electric Torrent (Recharge 5-6) The Body Snatcher unleashes a large electric pulse. Each other creature within a 20-foot sphere centered on the Body Snatcher must make a DC 15 Dexterity Saving Throw, taking 8d6 lightning damage on a failed save, or half as much on a successful one.