The Hagfish

There is an ooze which basks near recent battlefields, mass graves, and certain cemeteries, absorbing energies which emanate from rotting meat.

The Caravan

A group of traders discovered that, as the ooze moves to a new site, its puddle transforms into a portal big enough and which lasts long enough to drive a caravan through. They became famous for their fast journeys. They grew confident, and complacent, and now their caravan is only found near recent battlefields, mass graves, and certain cemeteries.

If you see them, you may notice that they can't shiver, can't walk backwards, and can't swallow. If you call out to them, they will repeat back to you whichever of your words seem most likely to make you leave. They have no tongues: their throats are full of butterflies, which puppet them, and drink blood. The puppets can kick twice as hard as a rifle shoots, and the swarm is happy to gain more puppets.

The now hundred-foot ooze coats the caravan's horses and wagons. What look from a distance like poles with pennants are spines, from which butterflies bud in sheets.

The ooze and the swarm are blind but possess an excellent sense of smell. The puppets spread out at twilight, to help the swarm forage; the puppets stand on one foot - with almost weeble-wobble balance - when empty. The ooze absorbs memories from the dead and its puppets can undertake any task those memories would allow.

The Herald

One member of the caravan, instead of becoming a puppet, was warped and sculpted into a misshapen ogre. He reclines on a bed of flying skulls, floating lazily backwards away from the caravan, announcing its presence on his oversized lute [edit: giant harp]. His great size and strength give his songs extra range.

He wears a large bearskin, has grown back the wrong number of arms, and - except for his ooze-filled veins - turns translucent when he casts spells.

Bolder or more desperate merchants sometimes seek him out to negotiate quick passages. He tries to sell them flasks of ooze. 

Certain Cemeteries

Liquefaction marks places where the ooze has puddle-ported - sand boils erupt, and the ground settles and flows unevenly, damaging whatever buildings and roads rest on it.

One town spotted a portal as it was forming and plugged it with debris; they don't realize the plug is slowly failing. Other towns have made their funeral practices more friendly to the ooze, because it preys on undead.

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Dragons are cool and all, but other animals are weird too. The puddle-porting is part Nydus Canal and part failed summoning circle, while the traders are inspired by these traders. 

Edit, May 24th: I have the vaguest impression that the butterflies-in-the-throat are like something I've heard before, and that the ooze's spines are similar to something else I've read before. The wagon train may be similar to a third thing, but all I recall about THAT was that the caboose contained a coffin which slowly transformed its unwilling occupant into a hag or something.