As a construct you cannot be poisoned, however attacks that can poison others can still damage you.
Your body gives you advantage on saving throws against being paralyzed.
You also have no need for sleeping, eating, or breathing.

You can add a d4 to one attack roll, ability check, or saving throw you make, and you can do so after seeing the d20 roll but before the effects of the roll are resolved. You can use this trait a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

You are encased in a thin metal or some other durable material. While you aren't wearing armor, your base Armor Class is 13 + your Dexterity modifier.

You are a construct and so long as you are not affected by a major injury such as losing a limb, being deactivated, or missing a part you can be healed by the mending spell. upon using mending gain 1d8 health. (cannot be used again in combat until 4 rounds have passed)
You can also benefit from Cure wounds, Healing Word, Mass Cure Wounds, Mass Healing Word, and Spare the Dying but reduced by half.

You are a construct and are not effected by spells specified for humanoids.

When you take a long rest, you spend at least 6 hours in an inactive, motionless state, instead of sleeping. In this state, you appear inert, but you remain conscious.

You gain two tool proficiencies of your choice, selected from the Player's Handbook

You have a +1 to Dexterity and +2 for any other ability score

Every day before you go into your inactive 6 hour rest you must perform maintenance and clean yourself. You must also have your clockwork rewound every day to keep running.
You can live indefinitely so long as you are rewound and get proper maintenance.
Every 4 months you must go to a tinkerer to be given a proper maintenance or risk damage to yourself which cannot be healed without getting parts replaced.

When you are hit by an attack which was a critical success the attacker rolls a d20 for the following effects.

1-10 nothing happens you just take a crit
11-12 you become incapacitated for 3 turns
13-14 you lose a random limb DM's choice or roll a d4 until someone puts it back on you (arm gives disadvantage to attack. Leg halves your movement)
15-16 you lose your head until someone puts it back on you (you are blind)
17-18 you lose a part from your body and cannot heal 1d4 health unless the part is replaced or put back
19-20 you are deactivated until someone repairs you (If this is rolled on a crit that takes you to 0 you die. But you explode dealing 4d10 damage to anyone within 20ft of you that fail a DC12 Dexterity saving throw)