Scalding Mud

This spell functions as transmute rock to mud (see page 295 of the Player's Handbook), except that it can be cast on sand, earth, and unworked, nonmagical rock (within the normal restrictions for transmute rock to mud), and the mud created is boiling hot.   Creatures mired in the hot mud take 5d6 points of fire damage per round, while those completely submerged in the sludge take 10d6 points of fire damage per round.   Creatures atop the mud (such as those standing on straw) take 1d6 points of fire damage each round from hot steam.   Damage from boiling mud continues for 1d3 rounds after exposure ceases, but this additional damage is only 1d6 points of fire damage per round.   The transmuted material cools after a period of 1 round per caster level.   The number of dice of damage the mud deals is halved each round after this duration expires.   The transmuted rock remains as mud even after it cools.   It eventually dries into soil, as per transmute rock to mud.   Arcane Material Component: A pinch of a mixture of clay, sulfur, and water.
 

You choose an area of stone you can see that fits in a 40-foot cube and that is within range, causing it to transmute to boiling hot mud. If you cast this spell on an area of ground, it becomes muddy enough that creatures can sink into it. Each foot that a creature moves through the mud costs 4 feet of movement, and any creature on the ground when you cast the spell must make a Strength saving throw. A creature must also make this save the first time it enters the area on a turn or ends its turn there. On a failed save, a creature sinks into the mud and is Restrained, though it can use an action to end the restrained condition on itself by pulling itself free of the mud.   Any creature that enters the mud for the first time each turn or starts its turn in the mud takes 5d6 Fire damage, or 10d6 Fire damage if they are Restrained by the mud. Any creature standing above the mud, such as standing on straw suspended in the mud or flying within 10 feet of the mud's surface, takes 1d6 Fire damage at the start of each of their turns from the hot steam.   If you cast the spell on a ceiling, the mud falls. Any creature under the mud when it falls must make a Dexterity saving throw. A creature takes 4d8 Bludgeoning damage and 5d6 Fire damage on a failed save, or half as much on a success. The mud does not remain thick enough after falling to continue causing damage as described above.   The mud cools off after a number of rounds equal to the level of the spell slot used to cast this spell, becoming normal mud.