TEXT: EN World EN5IDER| Battlefield Events
  Every fight is different, whether 
  that be due to the participants, the 
  weapons, the location, or even the 
  weather. A sudden gust of wind 
  or ground tremor, a wandering 
  monster attracted by the 
  commotion, or even a previously 
  undiscovered trap - all these 
  things can swing the tide of an 
  encounter. Fate and fortune, after 
  all, are as much part of battle as 
  are skill and planning.  This 
  article introduces battlefield 
  events - random events which can 
  happen on the battlefield, 
  affecting the combatants or the 
  environment. Battlefield events 
  add an additional element of 
  randomness into a battle.
  Using Battlefield Events
  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 on the table 
  on the next page to determine the 
  event (or the GM may choose 
  one).
  by 
  Russ Morrissey
  Russ Morrissey
  
  EN World EN5IDER | Battlefield Events
  Battlefield Events Chart (1d20)
  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. Depending on 
  the reason chosen, creatures with darkvision  may 
  still be able to see. Those who cannot see are 
  considered blinded. The effect persists for one 
  round.
  3.
  Innocent
  An innocent party unwittingly enters the 
  battlefield. This could cause a hostage situation, or 
  prompt good characters to protect the new arrival. 
  The innocent will be vulnerable (low level, young, 
  etc.).  
  4.
  Tremor
  A minor earth tremor forces all combatants on 
  the ground to make a DC 15 Dexterity save 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 it.
  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 
  random combatant gains advantage on his 
  next attack roll and automatically scores a 
  critical hit if the attack roll is successful. 
  Every combatant must roll 1d20, with the 
  highest rolling combatant gaining 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 
  outside, a 30-foot-tall tree falls in a random 
  direction, affecting a 5-foot-wide, 30-foot-long 
  area. If inside, the ceiling collapses at a random
  
  EN World EN5IDER| Battlefield Events
  location in a 15-foot-wide radius bury zone. 
  Those under the falling items take 22 (4d10) 
  bludgeoning  damage (or half that with a DC 
  15 Dexterity save).  The area underneath the 
  collapsed section then becomes filled with 
  rubble, and is treated as difficult terrain.
  9.
  Pit
  A 10-foot radius section of flooring or ground 
  gives way. Those on the area may make a DC 
  15 Dexterity save to avoid falling in. Those 
  who fall in take 4d6 bludgeoning damage 
  (2d6 falling damage and 2d6 from debris), 
  and are now prone in a 30-foot hole. 
  10.
  Press
  The flow of combat shifts the entire battle in a 
  random direction. Move all combatants 1d6x5 
  feet in a random direction. Nobody gains an 
  opportunity attack. If a character’s destination 
  square, or one en-route, is blocked, he must 
  make a DC 15 Dexterity save or fall prone.
  11.
  Extreme Favor
  For this round only, critical hits are scored on 
  a natural die roll of 19 or 20, and rolls of 1 do 
  not mean an automatic miss.
  12.
  Vermin
  The battle disturbs some small vermin living in 
  the area. A swarm of insects, rats, or other 
  appropriate vermin appears in a random 
  location and begins to move randomly across 
  the battlefield 1d6×5 feet in a random  
  direction each round. Rats cause difficult 
  terrain in a 10'x10' area; insects or bats cause 
  disadvantage on ranged attacks and Wisdom 
  (Perception) checks in the same area.
  13.
  Dust Devil
  A small whirlwind of dust moves across the 
  battlefield randomly. A 10-foot × 10-foot area 
  defines the dust cloud, and it moves 1d6×5 feet 
  in a random direction each round. Those 
  caught in the cloud must make a DC 12 
  Constitution save or be blinded for 1 round.
   
  14.
  Arcane Flash
  A burst of random residual spell energy, perhaps 
  left by a long dead archmage or deity, causes 
  magical powers to fluctuate. The next spell cast 
  by any combatant on the battlefield 
  automatically creates a Wild Magic Surge as per 
  the sorcerous origin.
  15.
  Trap
  A random combatant sets off a hitherto 
  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 rulebooks .
  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 fumble table below. See the next 
  page for fumble descriptions.
  17.
  Fatigue
  This battle is more grueling than most. All 
  combatants must make a DC 15 Constitution save 
  or gain one level of exhaustion until the end of 
  the combat encounter.
  Author - Russ Morrissey
  Editor - James Haeck
  Artist - Savage Mojo
  
  EN World EN5IDER | Battlefield Events
  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 
  — it was only a flesh wound! He is prone, but 
  actually has 50% of his normal hit point total. 
  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 rnaged 
  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, he fumbles instead 
  (see #16, above).
  20.
  A Really Bad Day
  Roll twice on this table.
  If a combatant suffers event #16 (Fumble), roll 1d6 to choose one of the following fumble events.
  1. Prone. The combatant slips or trips and
  falls prone.
  2. Disarmed. The combatant drops her
  weapon. If she is not holding a weapon, she 
  drops any other item held in her hand(s). If 
  she is not holding any items, she becomes 
  entangled (see below) instead.
  3. Entangled. The combatant gets caught up
  in foliage, furniture, curtains, or even his 
  own backpack. He gains the restrained 
  condition for one round.
  4. Vulnerable. The combatant makes a
  tactical mistake and places herself in a 
  vulnerable position. All attacks against her 
  gain advantage until the beginning of her 
  next round.
  5. Disoriented. A random blow, or a
  moment of confusion, effectively stuns the 
  combatant for one round.
  6. Blinded. Whether from blood in his eyes,
  or a helm falling down over his face - 
  perhaps even a bright light - the combatant 
  is temporarily blinded for one round.
  Fumble Descriptions
  
SOURCE: textdata/thevault/Dungeons & Dragons [multi]/5th Edition (5e)/3rd Party/EN World EN5ider/EN5ider 004 - Battlefield Events.pdf