Constructed Sentinel

Local Defender. Made to defend an area, the Sentinel cannot exceed a certain boundary through its own will.

Steam Discharge. Every 3 turns, the Sentinel discharges steam at the start of its turn. Its lower vents send the steam within 5ft, and the upper vents send the steam in a ring that is 15ft away. All creatures that are in the steam have to make a DC 13 Dexterity saving throw or take 1d8 fire damage. All non-magical flames are also suffocated by the steam.

Modular Armour. The Sentinel's armour has 3 additional plates attached onto it, concealing its vulnerable machinery. These can be discharged with the pressure of its steam, and has a return mechanism built inside. However, any creature that succeeds on a DC15 perception check, or has reason to understand its construction, can attempt to strike its attack at one of its armour pieces to dislodge it. On a hit, the armour piece gets knocked away by 10ft, and doesn't start moving until the end of the Sentinel's next turn. 

For each missing piece, the Sentinel's AC decreases by 2, and if even one is missing, it loses its resistance to piercing and slashing damage, and if two are missing then it is vulnerable to them. If all three are off, then it can no longer use its Steam discharge feature, or its Steam Shield reaction. However, its Dexterity score increases by 4.

Sweep. As an action, sweeps in a 90' arc with its sword. Those caught in its path must do a DC 15 dexterity saving throw, or take 2d8+4 slashing damage, and be knocked prone and pushed 5ft away.

Can only do this when rooted by its Spike Slam, and the area of effect cannot cross the spike.

Stomp. As an action, the Sentinel stomps in place, causing any creature within 5ft to make a DC 15 Strength saving throw or take 1d6 bludgeoning damage and be knocked back 10ft.

If they collide with a wall, they take 1d8 bludgeoning damage.

Spike Slam. Melee Weapon Attack: +4 to hit, reach 5-10ft., 1 target. Hit: 9.5 (1d10 + 4) piercing damage.

Immobilised until end of next turn. 

Shed Armour. Ranged Weapon Attack: +4 to hit, range 30ft., 3 targets. Hit: 9.5 (1d10 + 4) bludgeoning damage.

After using this attack, it's AC decreases by 2 for each missing armour piece, which will attempt to crawl back to it at a rate of 10ft per round, at the end of its turn. It can't use this again until at least one armour piece has returned.

Steam Discharge. As an action, sweeps in a 90' arc with its sword. Those caught in its path must do a DC 15 dexterity saving throw, or take 2d8+4 slashing damage, and be knocked prone and pushed 5ft away. Can only do this when rooted by its Spike Slam, and cannot cross the spike.

Steam Shield. If, next turn, it would've discharged steam, it can instead use it to interfere with a ranged attack, or ranged spell attack. As a reaction to either of these, it discharges the steam early and imposes disadvantage on the attack. 

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