Dead Man's Marsh

When you cast this spell, you conjure the pits of a hellish bog to the battlefield. You create a foul, miasmatic marshland terrain filled with bubbling, acidic liquid in a 30 ft radius sphere on the ground. When creature starts or ends it turn in the marshland area; it must make a Constitution saving throw. On a failed save, the creature takes 12d4 acid damage, plus 12d4 poison damage, and becomes restrained - sinking into the marsh. On a successful saving throw, a creature takes half as much damage with no restraint.
Creatures restrained by the marsh can use their Action to make an Athletics or Acrobatics check (their choice) to escape the marshland's muck that restrains it by making a save against the casters spell save DC. This infernal acid and poison damage bypass their respective resistances, and also negates poison immunity for the poison damage incurred by those that fail the saving throw. 

The marshland counts as difficult terrain, and all creatures within the area have their movement speed reduced by half. You cannot move the swamps area once casted - though its area spreads around corners. Recasting the spell allows you to change the swamps location.

When a creature dies in the marshland it will sink into the acidic liquid and all flesh melts off its bones, leaving only the skeleton and items, which will rise to the top.

This magic spell was created by the magi of wonder and whimsy; Cameron the Clairvoyant. He loved to create, and was inspired by many things around him - games, people, places, things, concepts, nature, anime, pop culture - and loved to craft superior unique things for the Dungeons and Dragons community. Check out his homebrew creations in every category on D&DBeyond, and feel free to incorporate them into your homebrew campaigns. Cameron the Clairvoyant is a former player-character that reached level 20 and now functions as a NPC Archwizard, and has created numerous impactful magic items, weapons, subclasses, monsters, creatures, feats and spells. Seek him out in your next quest! He loves to take requests and interact with parties of player-adventurers.