Gorgon

A gorgon on the party's side is a forge-construct, a guardian inherited with a deed to an old keep, or the prize from clearing a dwarven smith's vault. It is unaligned, mindless, and follows whatever simple instruction the party can give it through the bondings the original creator left behind. Treat it as siege equipment with hooves, not a companion.

The use case is one specific scene. The party knows they're walking into a fortified door with a Large enemy on the other side, and they need a battering ram that also bites. Send the gorgon through first. With a 40 ft. walk speed and the Gore charge condition, it can move 20 ft. and slam into a target for 18 average damage plus Prone if it's Large or smaller. Follow up the next turn with Trample as a Bonus Action against the prone target for another 16 average. That two-round combo will drop almost any single mid-CR adversary the party would otherwise have to fight head-on.

Petrifying Breath is the question you have to answer before the scene starts. The gorgon does not distinguish between friend and foe in a 30 ft. cone, and at DC 15 Con, the party's wizard is rolling at disadvantage even on a normal day. Tell the party where the cone will land before you call for the save, or position the gorgon at the front of a corridor where the party is behind it. A petrified PC is a scene-derailer; the player will not enjoy the four sessions it takes to find a Greater Restoration.

Once the door is down or the boss is on the floor, the gorgon stops moving. It stands where it stopped until someone gives it the next command, which is a great horror beat in an empty hallway. The party will keep glancing back at it.

A gorgon is a freight train with a poison ticket. It runs in straight lines, hits like a wagon, and turns whoever survives the first pass into a statue on the recharge. Place one in a meadow, a mine, or a temple courtyard with enough room for it to charge twenty feet, because the entire encounter assumes that opening movement.

Round one, the gorgon Gores. If it can move 20+ feet straight at the target, the hit knocks Large or smaller creatures Prone. Twenty-three average damage plus Prone on a single attack is ugly at CR 5, and on round two the gorgon follows up with Trample as a Bonus Action against the prone PC for another 16 average. A fighter eats 39 damage across two turns and spends a turn standing up. A wizard does not survive.

Petrifying Breath is the recharge clock the party has to respect. DC 15 Con save, 30 ft. cone, and the failure track is brutal: first failure Restrains, second failure on the next turn Petrifies. That's a two-turn save chain, so a PC who fails one needs help breaking the Restrained condition before the next save comes due. Counterspells and dispel magic do not work, since the gorgon has Immutable Form and that's a breath weapon, not a spell. The party's options are: drop the gorgon below 0 HP fast, or get the Restrained PC out of the cone before the second roll.

The retreat trigger is none. The gorgon is mindless, it does not flee, and it does not tactically reposition. It charges, it gores, it tramples, and it breathes when the recharge comes up. AC 19 and 114 HP make it a real wall, especially against a party that doesn't have piercing or slashing weapons handy.

Roll the Petrifying Breath recharge in the open at the start of each gorgon turn. The party will hold their breath every time the d6 drops.