Sixth sense. While the parasite inhabits the host a second heartbeat can heard by the host or any creature with sensitive hearing. The heartbeat becomes more rapid and panicked if the parasite feels in danger or senses something is wrong.

Creeping control. Should the host suffer anything that would stun, knock unconscious, or put the host in a state of any weakness. Then the host must make a CON Save DC:15 or they will lose a slight bit of control of their actions.

lvl 1: A scratching noise at the back of your skull constantly.

lvl 2: Voices of an unknown language whispering to you.

lvl 3: The whispers become somewhat coherent and every other word is understood. Allowing for the parasite to suggest a course of action that would favor the parasite.

lvl 4: Your actions and words can be slightly controlled.

lvl 5: Your have episodes of controls from the parasite for up to 30 min a day.

lvl 6: The parasite fully controls your body, the only hope of being saved is a forced surgery or a Piercing damage of 15 into the host near the heart.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., 1 target. Hit: (3d8 + 4) [Piercing] damage. STR Save DC:14 To prevent Pierce chest.

Manual control. The parasite uses its turn to slither into a viable corpse and control it. At the start of its next turn the parasite will control the corpse making it a Zombie. 

bite attack the parasite has two options.

lay egg. The parasite lays an egg within the bite victim. Should this not be removed within an hour, a parasite will hatch and the process starts again.

Assume control. The parasite more forcefully taps into the spinal cord to assume control over the bite victim. Victim can be any size. CON Save DC:13

Attack of Opportunity.