Iron Grappler

As an Autonomous Action (up to your proficiency bonus number of times per long rest) the Iron Grappler will use its straps as a shield (if its not grappling) and defend against attacks gaining a situational +5 AC bonus for that attack only.

At 10th Level: creatures with weapons must make a Strength or Dexterity Save or else be disarmed, other creatures will be knocked prone.

Cure Wounds or similar spells do not heal this construct, the Artificier's Repair ability can however.

The Iron Grappler will default to use dodge as its action; and disengage as its bonus - whenever it's not directed to engage. Attackers get disadvantage on attack rolls against it, and the Grappler counts as an ally for the purposes of flanking or rogue sneak attacks when within 10ft of the creature.

As the the artificer grows; add its Artificer's proficiency bonus to its:

Melee Weapon Attack: +2 to hit, reach 10ft., one target. *Hit* 3 (1d4 + 1) Bludgeoning damage. If the target is a creature, it must succeed on a (Large DC 8) (Medium DC 12) (Small DC 15) Strength or Dexterity saving throw or be knocked prone.

At 5th Level: Damage increases to d8; saving throw DC (Large DC 10) (Medium DC 14) (Small DC 16)

At 10th Level: Damage increases to 2d6; saving throw DC (Large DC 10) (Medium DC 16) (Small DC 18)

Despite its size the Grappler may attempt to grapple up Medium Sized creatures.

At 7th level it may attempt to Grapple Large Creatures;

At 11th level it gains advantage on Grappling attempts,

At 16th it may grapple up to 3 Medium creatures within 15 feet or each other.

Prone creatures that are Grappled are considered incapacitated.