Lava

When you enter a square that is within 20 ft of lava, you immediately take 2D4 fire damage. If you start your turn there, you take 2D4 fire damage and you must make a DC 12 CON save or suffer 1 level of exhaustion. Consecutive saving throws within this distance are made with disadvantage, but you can only gain 1 level of exhaustion from exposure to lava at this distance.
When you enter a square that is within 10 ft of lava, you immediately take 2D10 fire damage. If you start your turn there, you take 2D10 fire damage and you must make a DC 15 CON save or suffer 1 level of exhaustion. Consecutive saving throws within this distance are made with disadvantage, but you can only gain 1 level of exhaustion from exposure to lava at this distance. You also become disfigured by second-degree burns, and gain a disadvantage on CHA (persuasion) checks but advantage on all intimidation checks. These burns fade over the course of D6 days.
When you enter a square with lava, you take 6D10 fire damage. If you start your turn in lava, you take 10D10 fire damage and must make a DC 18 CON saving throw or suffer 1 level of exhaustion. These levels of exhaustion stack, as opposed to exhaustion by exposure at a distance. You also gain second- and third-degree burns all over your body, granting disadvantage on CHA (persuasion) checks but advantage on intimidation checks. These burns can be cured with a Greater restoration spell or similar magic.
When you are submerged in lava, you take 18D10 fire damage, and any non-magical equipment worn is destroyed. If you drop to 0 HP when you are submerged in lava, your body is destroyed and you can only be brought back to life by a Wish spell or similar magic.