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  Miscallaneous | Optional Rule: Sterling Vermin Initiative
  Optional Rule: Sterling 
  Vermin Initiative
  Following the release of the Greyhawk Initiative rules 
  via the official Unearthed Arcana article from Wizards 
  of the Coast, many people posted their own take or 
  variation on the concept. While the Greyhawk Initiative 
  system seems to have been developed to evoke an 
  old school style or incorporate traditional elements 
  of certain war games (with their ranged attack, melee 
  attack, and magic attack phases) it doesn’t incentivize 
  any new or interesting gameplay behaviors and 
  complicates decision making significantly. Many of 
  the other new variations people are producing are 
  alternative ways of doing an initiative system in D&D 
  5e without much of a sense of why the initiative system 
  would be different. Provided here is the Sterling 
  Vermin initiative system that attempts to improve the 
  strategy involved in decision making in 5e combat by 
  incentivizing less direct combat actions with better 
  initiative values.
  Overview                                                    
  Like the Greyhawk initiative variant, the Sterling Vermin 
  initiative variant changes some of the standard rules 
  found in the Player’s Handbook.
  Rounds. Combat is organized into rounds. Each 
  round, everyone involved in the combat has a chance to 
  move and take actions, as with standard initiative. But 
  the durations of effects are measured in rounds, rather 
  than ending during a specific creature’s turn.
  Variable Turn Order. Each round, every creature 
  involved in the battle rolls initiative. The order in which 
  creatures take their turns changes from round to round, 
  making it impossible to predict how events in combat 
  will unfold.
  Initiative Dice. Rather than always rolling a d20 for 
  initiative, characters and monsters might roll a variety of 
  initiative dice—from d4 to d20. The initiative die you roll 
  depend on the highest die associated with an activity 
  you took on your turn.
  Initiative Count. Under the standard system, 
  creatures with higher initiative have a chance to act 
  each round before creatures with lower initiative. With 
  this variant system, initiative now runs from low to high. 
  Creatures with a lower initiative roll can act in combat 
  before creatures with a higher initiative roll.
  Order of Operations. These rules make it more likely 
  for certain actions to take place earlier in a round, and 
  for other actions to take place later. Taking the Attack or 
  Cast a Spell action likely means a character or creature 
  will act later in the next round than someone who spent 
  their turn repositioning with Dash, avoiding enemies 
  with Dodge, or trying to Hide. As with the standard 
  initiative system, the luck of the dice always determines 
  exactly when combatants act.
  Rounds
  Combat under this system is divided into rounds, each 
  of which continues to represent about 6 seconds of 
  action.
  Durations. Any effect that normally lasts until the end 
  of a turn instead lasts until the end of the round during 
  which that turn takes place. Similarly, any effect that 
  normally lasts until the start of a turn now lasts until the 
  start of the round during which that turn takes place.
  If the order in which effects end is important for some 
  reason, roll a d20 for each effect (rerolling any ties). The 
  effect with the lowest roll ends first, with the others 
  ending in order of their results from lowest to highest.
  Surprise
  A surprised creature adds +10 to its initiative result and 
  cannot take reactions while it is surprised. A creature is 
  surprised until the end of the round during which it is 
  surprised.
  Determine Action Order
  During the first round of combat, all combatants 
  roll a d20 to determine initiative. Each round after a 
  combatant takes their actions, the combatant rolls 
  their initiative for the next round using an initiative die 
  determined by the actions they took this round.
  Actions are broken down by speed. Because a lower 
  initiative count allows a creature to act more quickly, 
  fast or simple actions use smaller dice and more 
  complex actions use larger dice.
  When rolling initiative, you roll only the single highest 
  die associated with all the actions you took on your turn. 
  You do not add any modifier (including your Dexterity 
  modifier) to this roll.
  Initiative Dice
  Reactions and Forced Activities. Initiative covers 
  only the actions you take on your turn, so that using a 
  reaction has no effect on your initiative. You can take 
  one reaction per round, as normal, unless an ability 
  grants you more.
  Likewise, any activities you are forced to undertake 
  not on your turn (typically in response to another 
  creature’s actions) have no effect on your initiative.
  Delaying. You cannot use the Ready action under 
  these rules, but you can instead choose to delay your 
  turn. Instead of taking your turn on your initiative 
  count, you simply act on a later initiative count, before 
  or after other creatures as you choose. If more than one 
  creature has chosen to delay, each creature’s original 
  initiative needs to be noted. Whenever a delaying 
  creature decides to act, another delaying creature with a 
  lower initiative can decide to act immediately before it.
  Creatures Unable to Act
  Any creature that is unable to take actions (most likely 
  because it is incapacitated) rolls a d20 for initiative.
  Choosing Another Creature’s Actions
  If you are in a position to choose the actions that 
  another creature takes on its turn (for example, if 
  you have successfully targeted that creature with the 
  dominate monster spell), you roll initiative for the 
  creature as normal using the initiative die indicated by 
  the actions that creature took on its turn.
  Attack, Cast a Spell
  Dodge, Hide
  Help, Search, Use an Object
  Dash, Disengage
  Move, a bonus action
  __
  d20
  d12
  d10
  d8
  d6
  d4
  InItIatIve DIce
     Die      Action
  
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  Miscallaneous | Optional Rule: Sterling Vermin Initiative
  Ties
  If two creatures tie for initiative, those creatures act in 
  order of Dexterity, with the highest Dexterity going first. 
  If both creatures have the same Dexterity, roll randomly 
  to determine which one acts first.
  Special Rules
  Certain effects can alter initiative rolls in the game.
  Initiative Bonuses or Penalties. Though this system 
  does not apply a creature’s Dexterity modifier to its 
  initiative rolls, other effects can alter initiative. If an 
  effect would grant you a bonus to your initiative roll 
  under the standard system, instead reduce the size of 
  one die you roll for initiative, by moving two die sizes 
  down on the initiative dice table above.
  In the case of a penalty to your initiative, you apply the 
  reverse process, increasing the size of one die rolled by 
  moving to die sizes up on the initiative dice table above.
  Advantage or Disadvantage. If an effect would grant 
  you advantage or disadvantage on your initiative roll 
  under the standard system, roll your initiative die twice, 
  using the lowest roll if you have advantage or the highest 
  roll if you have disadvantage.
  Optional Rule: Sterling Vermin Initiative by
  Benjamin Huffman
  http://sterlingvermin.com/
  
SOURCE: textdata/thevault/Dungeons & Dragons [multi]/5th Edition (5e)/3rd Party/Benjamin Huffman/Vermin Initiative.pdf