As the party settles into Ravine’s Parched Pilgrim Tavern for the evening, their adversaries have a small surprise waiting for them—sometime in the middle of the night, the P.R.A.N.K.S.T.ER.S. launch a twilight ambush on the sleeping adventurers!
The attack starts when the majority (if not all) of the spellcasting PCs are asleep. Creatures that are still slumbering are targeted with a nightmare spell (DC 18 Will negates). Immediately thereafter, ten P.R.A.N.K.S.T.E.R. hirelings teleport into the area and attack. The assault is mainly a diversion—the cabal’s agents in the Grave Morass are observing the combat, taking note of the tactics and spells used by the party in order to optimize their own defenses for a conflict they’ve decided is inevitable. This offensive has an ulterior motive, however; each hireling has a wand of hostile morass (2 charges) which the criminals try to use on each party member at least once (DC 18 Will save negates). Agents in the Grave Morass are watching from afar with a scry spell (DC 24 Perception check to notice) and take note of any special attacks used by the party, preparing their defenses accordingly.

The P.R.A.N.K.S.T.E.R.S. specifically developed the special hostile morass spell and provided the wands to these hirelings.

HOSTILE MORASS
School abjuration [evil]; Level sorcerer/wizard 4
Casting Time 1 standard action
Range close (25 ft. + 5 ft. / 2 caster levels)
Target creature touched
Duration 1/day per caster level
Saving Throw Will negates; Spell Resistance yes
Hostile morass is only active while the target is in the Grave Morass of the Scorched Lands. While in the Grave Morass, a creature that fails its Will save suffers the following effects:
     Attract Ash The creature attracts the ash from the Grave Morass, taking a -2 penalty to Dexterity-based abilities and effects, treats all terrain is treated as difficult terrain, and their base movement rate is halved. The ash can be removed with a full round action but 1d6+1 rounds later it accumulates again.
     Attract Oil The creature attracts the oil from the Grave Morass, coating their body in a thin layer of the viscous liquid. Any open flames or fire-based effects that happen within 5 ft. of the creature cause it to catch on fire (taking 1d6 points of fire damage each round). It takes a full-round action to extinguish the flames.
     Attract Sand The creature attracts the sand from the Grave Morass, taking a -4 penalty to concentration checks.
These effects cannot be dispelled, but they can be removed with a break enchantment, limited wish, miracle, remove curse, or wish spell.

5E Rules

The P.R.A.N.K.S.T.E.R.S. cast dream instead of nightmare.
Locating the sensor of the scrying spell requires a DC 30 Wisdom (Perception) check.

HOSTILE MORASS
5th-level abjuration
Casting Time: 1 action
Range: 60 feet
Components: V, S
Duration: 1 week
You wrap a creature in energies that draw upon the primal fundament of the Grave Morass, causing it to attract the very landscape of that region in the Scorched Lands of Aventyr. A creature targeted by this spell must succeed on a Charisma saving throw or suffer from the following effects:
     The creature attracts ash from the Grave Morass, reducing its movement speeds by half. Removing the ash requires an action and it accumulates again after 1d4 rounds.
     Oil coats the creature, causing it to ignite and take 1d6 points of fire damage each turn until it or another creature spends an action putting out the flames.
     Sand inexorably draws toward the creature, causing it to take disadvantage on Perception checks.
These effects cannot be removed with dispel magic, but they can be removed with a remove curse or wish spell.