Terrain
Listed below are the various terrain features I use when designing dungeons and battlefields.
Demonic Impulses – Once per day, when a sentient creature passes though a cursed area, they get strong impulses to lash out at their companions or themselves, making a DC 8 Wisdom saving throw.
On a failure, they take 3d6 psychic damage and verbally abuse themselves or another member of the party, forcing each sentient creature within earshot to make this saving throw. On a pass, they take half as much damage and do not verbally abuse their allies.
If a hero would be reduced to 0 hit points by this damage, they are instead reduced to 1 hit point and are compelled to physically abuse the closest ally. On their turn, they must move towards the closest ally and use the Attack action against them (they may use unarmed attacks). At the end of each of their turns, they make a new saving throw to end this effect on themselves.
Ledge – A rough ledge that a hero must jump down from or mantle over. Crossing a ledge is difficult terrain. Whenever a hero crosses a ledge, they take 1d4 fatigue damage unless they pass a DC 8 Strength (Athletics) check.
Quartz Deposit – A mineral deposit containing significant amounts of alchemically pure quartz. A spellcaster using detect magic senses the aura of the deposit as faint Divination (Clairvoyance). Actively examining the deposit reveals any other quartz deposits within 100 yards, and the caster can link divination spells between two deposits.
A hero can spend 10 minutes harvesting a quartz deposit, collecting pounds of quartz ore equal to their Wisdom modifier (minimum 1/2). If the hero is proficient with alchemist’s vials or the miner’s pick, they add their proficiency bonus to the number of pounds collected.
Rubble – A large pile of loose stones and debris that can’t easily by bypassed. Squeezing into rubble requires an action.
If a hero enters the rubble or starts their turn there, they become grabbed by it and their turn ends unless they pass a DC 8 Strength (Athletics) check.
Escaping rubble requires the Escape action and a DC 8 Strength (Athletics) check. On a failure, the hero becomes restrained by the rubble and takes 1d8 crushing damage.
A hero can spend 10 minutes and attempt a DC 8 Strength (Athletics) check to clear the rubble. On a pass, they take 1d4 fatigue damage and the rubble is cleared. On a failure, they take 1d4 fatigue damage and the rubble remains. If they roll a 1 on the d20, they cause a cave-in.
Scree – Sharp rocks that are loose and easy to slip and slide on. Typically found in caves and mountainsides, scree is difficult terrain. Anyone who falls prone in scree takes 1d4 slashing damage (or 2d4 if they used the Dash action this turn).
A hero can attempt a DC 8 Dexterity (Acrobatics) check to move over scree at full speed. Failure causes them to fall prone and ends their turn.
Standing Water – Any standing water is difficult terrain and a creature is vulnerable to cold and lightning damage while in standing water. If a creature falls prone in standing water, they are soaked, making them vulnerable to cold and lightning damage until they dry out (usually as part of a short rest).
A hero can attempt a DC 8 Strength (Athletics) check to move through standing water at full speed. Failure causes them to fall prone and ends their turn.
Unsettling Warning – Explorers love to leave unsettling warnings on the walls of haunted and cursed places. Reading an unsettling warning gives the heroes some insight into the dangers of the location, but also deals 1d12 morale damage (DC 8 Charisma saving throw for half).
If a creature would be reduced to 0 hit points by this damage, they are instead reduced to 1 hit point and are rattled while in the location until they finish a short rest. If they were already rattled, they instead become frightened of the location until they finish a short rest.