TEXT: Blade Oils
  Some warriors like to plan ahead, arming themselves for
  battle against specific types of enemies. Blade oils allow a
  combatant to prepare their weapon to destroy a certain
  category of foe. Blade oils consist of a two part alchemical
  formulation:
  One is rubbed into the weapon over the course of a short or
  long rest. Forcing the warrior to decide ahead of time what
  they will need.
  The other, as a Bonus Action, is poured over the weapon
  during battle to catalyse the reaction and activate the oil.
  Ingredients
  Blade Oils are defined by their ingredients, anyone with a pot
  can mix an oil if they know how. Exact ingredients can be
  determined by the DM ahead of time or left to the player
  creativity.
  Binding Agent
  The binding agent ties the oil together, allowing it to bond
  with the surface of a blade, bludgeon or arrow-heads. The
  binding agent is a the first thing you can use to control the
  availability of oils in your campaign. They can be fairly
  ubiquitous, if you want your players to have constant access
  to blade oils. Or if you prefer the oils be something more
  carefully considered, they can be a rare or costly material.
  Examples of potential binding agents include Adhesives,
  Thick Oils, Vines and Roots
  Honing Agent
  The honing agent determines the creature type to which the
  oil applies its effect. It also determines the potency of the oil's
  effect. The honing agent is either purchased or harvested
  from a defeated creature.
  The applicable creature types for oils are Aberration,
  Beast, Celestial, Construct, Dragon, Elemental, Fey, Fiend,
  Giant, Monstrosity, Ooze, Plant, and Undead. When a weapon
  with a catalysed blade oil hits an enemy of the chosen type, it
  deals bonus damage according to its potency.
  (Humanoid is excluded for balance purposes, but could be
  included if the DM want's to tweak the cost or include
  societal implication for using it.)
  The potency of a blade oil is determined by the CR of the
  creature from which the Honing Agent was harvested.
  Potency
  CR
  Damage Bonus
  1 or less
  1d4
  2 - 4
  1d6
  5-7
  2d4
  8+
  2d6
  If blade oil is used against a creature of precisely the same
  type as the honing agent was harvested, the damage bonus is
  increased by one die of the appropriate size. (For example, oil
  made with Vampire dust would deal 3d6 damage to
  vampires, and 2d6 damage to other undead.)
  Priming Agent
  The priming agent gives the oil it's power and is the source of
  the extra damage. The choice of priming agent allows the
  player to choose the damage type of their oil. This is another
  area where the DM can control the effectiveness of oils to
  suit their campaign. The basic elemental damages are
  generally solid bets, but allowing easy access to force, psychic
  or radiant damage might be worth avoiding.
  It is worth considering that some combinations of damage
  type and creature type could synergise well. For instance, a
  blade oil honed to plant creatures that deals fire damage is
  likely to be extremely effective.
  You might consider having player characters learn about
  priming agents through experimentation, and restricting the
  bonus damage to match the weapon type until they figure it
  out. You can always restrict access to damage types by
  specifying specific, rare ingredients and limiting your players'
  access to them.
  Catalysing Agent
  This is where I recommend adding in an element of skill
  checks. When a character makes themselves a blade oil,
  allow them to simply gather and combined the ingredients
  without making a check. It would feel bad to harvest parts
  only to ruin them in the creation process.
  When the character makes the catalust however, ask for an
  ability check. Using your choice of ability score and
  proficiency in Alchemist Supplies, Herbalism Kit, Brewing
  Supplies, anything that makes sense. Have this check
  determine the duration that the catalyst activates an oil for.
  Duration
  Score
  Damage Bonus
  1-5
  1 Round
  6-10
  2 Rounds
  11-20
  1 Minute
  21+
  1 Hour
  If you don't want them to keep making the check over and
  over again, apply a cost here in the form of time, gold or both.
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  DarkAbyssKeeper and published under the Community
  Content Agreement for Dungeon Masters Guild.
  
SOURCE: textdata/thevault/Dungeons & Dragons [multi]/5th Edition (5e)/3rd Party/DMsGuild/Quick and Dirty Blade Oils.pdf