Shield Guardian

A shield guardian is a 142-HP construct bodyguard, and the entire fantasy is "I have an iron golem who follows my wizard around and refuses to let them die." The guardian is bound to an amulet, the amulet's wearer can telepathically call it across the same plane, and the wearer can store one spell of level 4 or lower inside it for later cast. Treat it as the wizard's second action economy.

Run the Bound trait at the table. While the wearer is within 60 feet of the guardian, half of any damage the wearer takes (round up) transfers to the guardian. That changes the math on every dragon's breath weapon: the wizard takes half, the guardian eats the other half on top of its 142 HP, and the guardian regenerates 10 HP at the start of every turn so long as it has at least 1. A party with a shield guardian gets to walk the wizard into the breath cone on purpose. Plan encounters knowing this.

Spell Storing is the second bag of tricks. Park a Fireball, a Banishment, a Greater Invisibility, or a Polymorph in the guardian during downtime, and the guardian casts it on the wearer's command using the original caster's DC. The stored spell uses no components and costs the guardian no action economy. One spell at a time, lost on overwrite, so the wizard chooses fresh each morning.

In melee, Multiattack is two Fists at +7 for 18 each (11 bludgeoning, 7 force). The 10-foot reach lets the guardian stand between the wizard and the front line and threaten a wide arc. Protection as a Reaction adds +5 AC to the wearer against one attack so long as the guardian is within 5 feet, and the immunities (Charmed, Exhaustion, Frightened, Paralyzed, Petrified, Poisoned) mean a Hold Person on the wizard does nothing to the bodyguard. The party should feel like the wizard cannot actually be killed unless the enemy spends a full round dismantling the construct first.

Have the guardian speak through the wearer. It cannot talk, but it understands every command. A stored Sending each morning is the closest thing it gets to a voice, and players will cherish that detail.

A shield guardian as adversary is almost always a guardian still standing watch over a master who has died, gone mad, or sold the amulet to the wrong person. The classic setup is a tomb where the original wizard's body is centuries gone but the construct keeps patrolling because no one ever issued the order to stand down. A second is a current owner who is the actual villain: get to the wearer and the guardian becomes a tactical problem with a clear shut-down condition.

If the wearer is on the field, run the guardian as the bodyguard from the ally tab and play it ruthlessly against the party. Bound transfers half damage off the wearer onto the construct, Protection gives +5 AC against one attack per round, and Multiattack throws two Fists at +7 for 18 each on whoever closes with the wearer. The party's correct play is to identify the amulet, target it directly, or grapple the wearer out of the 60-foot range. Tell them the amulet glows when Bound triggers; this is information, not a hint.

If there is no wearer, the guardian patrols a fixed area and will not pursue past it. Run it as a heavy: 142 HP, AC 17, Regeneration 10 per turn means attrition fights are losing fights. The party needs to deal more than 10 damage per round just to make progress, and any round they do not is a round given back. The condition immunities shut down most control options. Force damage in the Fist hits ghosts and walls equally; the guardian was built to break things.

Place the amulet visibly on the chain of an NPC the party might want alive. Make killing the wearer the cost of stopping the construct. The choice is the encounter.