Might of the Master. The following numbers increase by 1 when your proficiency bonus increases by 1: the steamjack's skill and saving throw bonuses (above), the bonuses to hit and damage of its slam attack, and the number of hit points restored by its Repair action (below).

Vigilant. The defender can’t be surprised.

Steamjack. In combat, the steamjack shares your initiative count, but it takes its turn immediately after yours. It can move and use its reaction on its own, but the only action it takes on its turn is the Dodge action, unless you take a bonus action on your turn to command it to take one of the actions in its stat block or the Dash, Disengage, Help, Hide, or Search action.

Ferrum-Grade Cortex. The Nomad’s cortex allows it to understand basic commands from its controller (spoken verbally by most but usually communicated telepathically by warcasters). Verbal commands must be akin to those issued to a trained animal, such as “stay,” “guard,” “attack,” and so on. The Nomad will carry out these commands with no regard for its own safety. 

More complicated orders require careful guidance from a ’jack marshal. A steamjack with a ferrum-grade cortex learns to follow instructions fairly quickly. Over time, it improves its ability to execute simple tasks and develops a limited personality.

A steamjack with a ferrum-grade cortex has an Intelligence score of 5, a Wisdom score of 10, and a drive DC of 15. The ferrum-grade cortex grants the steamjack a +2 proficiency bonus and it is proficient in the Athletics skill.

Heavy Metal. The Nomad’s attacks are magical for the purpose of overcoming resistances and immunity to nonmagical attacks for steamjacks, colossals, and warbeasts.

Steam Powered. The Nomad requires coal and water to function. When not in combat, it can function for 5 hours with a full fuel load of 660 pounds of coal and fresh water in its boiler. While in combat, the Nomad can function for 1 hour with a full fuel load. If the Nomad’s coal and water are not refilled at the end of this time, it suffers one level of exhaustion at the end of each minute. Due to the amount of noise its steam engine produces, the Nomad has disadvantage on Dexterity (Stealth) checks.

Water Vulnerability. A steamjack’s reliance on burning coal means that unless it has specifically been designed for underwater operations, being submerged in water or having its firebox doused is a surefire way to shut it down. If a steamjack is fully submerged or its firebox is exposed to a sufficient amount of water (as determined by the GM), its boiler becomes extinguished, rendering the steamjack inert.

Tried and True. When the Nomad regains hit points, it regains 5 additional hit points.

If the mending spell is cast on it, it regains 2d6 hit points. If it has died within the last hour, you can use your smith’s tools as an action to revive it, provided you are within 5 feet of it and you expend a spell slot of 1st level or higher. The steel defender returns to life after 1 minute with all its hit points restored.

Slam. Melee Weapon Attack: +4 to hit, reach 10 ft., one target you can see. Hit: 1d8 + 2 bludgeoning damage.

Heavy Drill Rig. Melee Weapon Attack: +4 to hit, reach 10 ft., one target you can see. Hit: 2d10 + 2 piercing damage.

Scrap Saw. Melee Weapon Attack: +4 to hit, reach 10 ft., one target you can see. Hit: 2d6 + 2 slashing damage.

Repair (3/Day). The magical mechanisms inside the defender restore 2d8 + 2 hit points to itself or to one construct or object within 5 feet of it.

Deflect Attack. The defender imposes disadvantage on the attack roll of one creature it can see that is within 5 feet of it, provided the attack roll is against a creature other than the Docker.