Random Battlefield Events

Fate and fortune are as much part of battle as are skill and planning. Every fight is different, whether because of the participants, the weapons, the location, or even the weather. A sudden gust of wind or ground tremor, a monster attracted by the commotion, or even a previously undiscovered trap—all these things can swing the tide of an encounter. This article introduces battlefield events: random events that can happen during a battle and that affect the combatants or the environment. Battlefield events add an additional element of randomness into a battle.

Battlefield events are easy to implement during a combat encounter. At the beginning of every round, simply roll 1d20. On a roll of 20, a battlefield event takes place. Roll 1d20 and consult the table to determine the event, or choose one that you find appropriate.

d20	Event
1	Gust of Wind. A strong gust of wind suddenly blows across the battlefield. The force of the gust automatically extinguishes candles, torches, and similar unprotected flames. It causes protected flames, such as those of lanterns, to dance wildly and has a 50% chance to extinguish those lights. Ranged attack rolls and non-magical flight are not affected, because the gust is too brief. In addition to the effects noted, a gust of wind can do anything that a sudden blast of wind would be expected to do. It can create a stinging spray of sand or dust, fan a large fire, overturn delicate awnings or hangings, heel over a small boat, and blow gases or vapors to the edge of its range.
2	Visibility. An environmental effect limits visibility. The cause of this depends on the location—it may be the closing of a window or door, clouds obscuring moonlight, a sudden heavy fog or sandstorm, or the failure of magical lighting. The battlefield becomes heavily obscured for 1 round. Depending on the reason chosen, creatures with darkvision may still be able to see.
3	Innocent. An innocent party unwittingly enters the battlefield. This could escalate into a hostage situation, or it might prompt good characters to protect the new arrival. The innocent will be vulnerable (for example, low in level or young).
4	Tremor. A minor earth tremor forces all combatants on the ground to make a DC 15 Dexterity saving throw or fall prone.
5	Weather. It begins to rain or sleet heavily (depending on the environment). The weather lightly obscures vision, and all creatures on the battlefield suffer disadvantage on sight-based Wisdom (Perception) checks; if the weather is rain, this also applies to hearing-based checks. The weather extinguishes open flames. In the case of sleet, the ground becomes slippery for the rest of the encounter, requiring all creatures to succeed on a DC 10 Dexterity (Acrobatics) check to avoid falling prone the first time they attempt to move on each of their turns.
6	Monster. A random monster, attracted by the sounds of battle, enters the battlefield, attacking combatants at random. The monster(s) are selected by the GM and should be of a challenge rating equal to half the party’s level.
7	Touch of Favor. Whether due to luck or to divine favor, one randomly determined combatant gains advantage on its next attack roll and automatically scores a critical hit if the attack roll is successful. Every combatant rolls 1d20; the highest rolling combatant gains this benefit. If there is a tie, all combatants in the tie gain the benefit.
8	Collapse. There is a major structural failure nearby. If the battle is taking place outdoors, a 30-foot tall tree falls in a random direction, affecting a 5-foot wide, 30-foot long area. If the battle is taking place indoors, the ceiling collapses at a randomly determined location, creating a 15-foot radius bury zone. Anyone in the affected area takes 22 (4d10) bludgeoning damage (or half that with a DC 15 Dexterity saving throw). The affected area is filled with rubble and is treated as difficult terrain.
9	Pit. A 10-foot radius section of flooring or ground gives way. Each creature in the area makes a DC 15 Dexterity saving throw or falls 30 feet down, taking 7 (2d6) bludgeoning damage from debris and 10 (3d6) bludgeoning damage from falling, landing prone in a 30-foot hole.
10	Press. The flow of combat shifts the entire battle in a random direction. Move all combatants 1d6 × 5 feet in a random direction. This movement does not provoke opportunity attacks. If a creature strikes an object, such as a wall or floor, it makes a DC 15 Dexterity saving throw or is knocked prone.
11	Extreme Favor. For this round only, attacks score a critical hit on a roll of 19 or 20, and rolls of 1 do not mean an automatic miss.
12	Vermin. The battle disturbs a colony or pack of vermin living in the area. Insects, rats, or some other appropriate vermin appear in a random location and begin to move randomly across the battlefield, moving 1d6 × 5 feet in a randomly determined direction each round. The vermin fill a 10-foot by 10-foot square area; rats create difficult terrain, and creatures in an area of bats or insects have disadvantage on ranged attacks and Wisdom (Perception) checks.
13	Dust Devil. A small whirlwind of dust moves across the battlefield. The dust cloud fills a 10-foot cube that moves 1d6 × 5 feet in a randomly determined direction at the start of each round. When a creature starts its turn in the area or first enters into the area, it makes a DC 12 Constitution saving throw or is blinded for 1 round.
14	Arcane Flash. A burst of random residual spell energy, perhaps left by a long-dead archmage or deity, causes the power of magic to fluctuate. The next spell cast by any combatant on the battlefield automatically causes a surge of wild magic (as the sorcerous origin).
15	Trap. A random combatant sets off an undiscovered trap. All combatants roll 1d20; the highest-rolling combatant sets the trap off. The GM selects a trap of setback severity from the core rulebook.
16	Fumble A random combatant fumbles. All combatants roll 1d20; the highest rolling combatant is the one who fumbles. If there is a tie, both combatants fumble. Roll 1d6 on the Combat Fumbles table above.
17	Fatigue This battle is more grueling than most. All combatants must make a DC 15 Constitution saving throw or gain one level of exhaustion that lasts until the end of the combat encounter.
18	I’m Getting Better A combatant who has been downed is not as badly injured as it appeared at first. All downed (dead or dying) combatants roll 1d20. The highest rolling combatant recovers: the combatant is prone and at half its hit point maximum. If there is a tie, all combatants in the tie recover in this manner.
19	Fatal Mistake A random combatant makes a dangerous mistake and receives a critical hit from the nearest opponent able to do so (either ranged or melee). All combatants roll 1d20—the highest rolling combatant is the one hit (both in a tie). The hit is automatic. If no combatant is in a position to hit the combatant in question, it fumbles instead (see #16, above).
20	A Really Bad Day Roll twice on this list.