Xorn

A xorn on the party's side is a mining contract with teeth. The framing is straightforward: the dwarf NPC who runs the local quarry has a xorn on retainer for tunnel collapses and gem location, the party is escorting it to a new claim, or a wizard's bound elemental servant tunnels ahead of the party as a scout. Xorns speak Primordial (Terran) only, so plan a translator or a comprehend languages spell.

In combat the xorn is a Tremorsense 60 ft. ambusher that should always strike from below. Tell the player or table running it to Earth Glide under the encounter and erupt with Charge plus Multiattack into the back rank: 41 average damage in one round on a CR 5 ally is excellent value. After the strike, it sinks back into the floor for one round and surfaces somewhere else. AC 19 and 84 HP let it tank a couple of rounds in melee if it has to, but the xorn prefers ambush over slugfest. Poison immunity, Paralyzed immunity, and Petrified immunity mean it shrugs off most low-tier debuffs the enemies will throw at it.

The xorn wants paying in metal and gems. A handful of silver pieces buys an hour of work. A gold piece buys a day. Magic items make it nervous and happy at the same time, and it will ask to gnaw the corner of a +1 longsword as bonus pay. Refuse politely; agree at your peril.

Roll a die for what the xorn keeps in its gullet. The party should always be slightly worried about what it has already swallowed.

A xorn is a CR 5 mugger that lives in the floor. AC 19, 84 HP, Earth Glide through unworked stone, Treasure Sense out to 60 ft., Tremorsense 60 ft., and a Multiattack of one Bite plus three Claws (17 + 8 + 8 + 8 average for 41 a turn). The whole encounter is the surprise from below. Run the xorn as the consequence of carrying a sack of gold through a cave.

Open with Earth Glide and Charge. The xorn senses the party's coin from 60 feet through stone, burrows under the floor of whatever passage they're walking, and erupts straight up into the marching order. Charge is a Bonus Action half-Speed dash toward an enemy it can sense, so the xorn gets full Multiattack on the round it surfaces. Target the PC carrying the most platinum, gems, or magical metal, because Treasure Sense tells the xorn exactly who that is. The party with a wealthy cleric will find that cleric in the air, in a mouth.

Once the bite lands, the xorn does not stay to brawl. AC 19 is solid but 84 HP melts under focused fire from a tier-2 party, so it grabs what it can and dives back into the floor. Earth Glide does not disturb the stone, so the players cannot dig after it unless they have stoneshape, dispel magic on the burrow, or a way to track through 20 ft. of granite. If the party blocks its escape with magic or with a worked-stone barrier (Earth Glide is unworked stone only), the xorn fights to half HP and then tries to surface elsewhere. It is Neutral with Int 11, which means it will negotiate. Offer a chunk of gold and the xorn might leave them alone for an hour.

Have the xorn surface mid-sentence. A player explaining the loot split goes flying. The shock is half the fun, the loot drama is the other half.