Hazard

A Hazard is an environmental effect that causes harm, hindrance, or both. Hazards differ from monsters and traps in that they are typically passive features of the environment that affect any creature exposed to them — friend and foe alike.

Categories of hazards:

• Damage hazards: lava, acid pools, falling debris, freezing water, Burning (catching fire), suffocation
• Movement hazards: difficult terrain, ice, mud, dense webs, dense forest
• Visibility hazards: Heavily Obscured fog, darkness, smoke
• Magical hazards: wild magic zones, antimagic fields, planar instability
• Climbing and falling: sheer cliffs, slippery surfaces, fall damage from height

How hazards interact with the rules:

• A hazard usually triggers on entry, on a specific action, or each round a creature remains exposed
• Saving throws or ability checks can mitigate or avoid the effect
• A hazard does not roll initiative; it acts as a feature of the environment that the DM applies at the appropriate moments
• Some hazards are creatures-in-disguise (a green slime, a yellow mold) and use stat blocks; these straddle the hazard/creature line

Designing for hazards: Hazards reward planning and environmental awareness. Telegraphing a hazard (visible scorch marks, the smell of sulfur, a corpse impaled on spikes) lets the party avoid or use it tactically rather than feel ambushed by DM fiat.