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

Multiattack. The symbiont makes one Bite attack and uses its Tendril.

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 10 (1d8+6) piercing damage plus 9 (2d8) acid damage.

Tendril. The symbiont lashes out at a creature within 10 ft. of it. The target must make a DC 16 Constitution saving throw. On a failure, the target is Paralyzed until the end of the symbiont's next turn. On a success, the target has disadvantage on Constitution saving throws until the end of the symbiont's next turn.

Make Host (Recharge 6). The symbiont targets a creature within 5 ft. of it that is Paralyzed. If the target is not a Construct, it must succeed on a DC 14 Intelligence saving throw or the symbiont enters the target's space, and attaches itself to the target. While the symbiont is attached to the target, the target takes any damage that the symbiont would receive. The symbiont can attach itself to only one target at a time.

The attached symbiont can telepathically control the target's movement and actions. While controlled in this way, the target can only take the Attack action, (the symbiont chooses the target) or the Dash action. If the attached target has an Intelligence of 10 or higher, it can repeat the saving throw at the end of every 24 hours until it succeeds. If the attached target has an Intelligence of 14 or higher, it can repeat the saving throw at the end of every hour, instead of every 24 hours, until it succeeds. On a successful saving throw, the symbiont is detached, and is forced into the nearest unoccupied space.