Apocalypse Blade

Apocalypse Blades can take many forms - one may be a holy weapon, delivering divine judgement against the enemies of a chosen god. Another may be a devilish weapon... intent on consuming souls. What they all have in common, is their distinct, supernatural drive to eradicate a certain type of creature from the mortal planes, fueling it's completion with the souls of those it is meant to destroy.

When an Apocalypse Blade is created, the DM chooses three creature types. This weapon's effects only apply against creatures of those types.

This weapon has a +3 bonus to attack and damage rolls made against the chosen creature types. 

When a creature of one of the chosen creature types dies within a minute after being damaged by the Apocalypse Blade, the blade shatters their soul, absorbing part of it's essence. Every time the blade absorbs 20 souls, it permanently gains one of the following properties, determined by rolling a 1d100. If you roll a property the blade already has, roll again.

After it gains it's first property, it no longer feels satisfied with low level creatures. The Blade will only absorb the souls of CR 15 or greater creatures.

After it's second property, the Blade will only absorb the souls of CR 20 or greater creatures.

After it's third property, the Blade will only absorb the souls of CR 20 or greater creatures that have Legendary Actions.

When the blade would gain it's fourth property, it automatically gains the final property on the table below.

Apocalypse Blade Properties
d100	Property
1-40	Attacks against the chosen creature type by this weapon do an extra 1d8 damage, with the damage type being determined by your own creature type. (Celestial does Radiant, Fiend does Fire, and Aberration does Psychic).
41-60	If you are forced to make a Saving Throw by one of the creature types that were selected, add +3 to your Saving Throw.
61-70	When you land an attack on a creature of the chosen type using this weapon, you may spend and roll any number of your unspent Hit Dice. Add the total rolled to the attack's damage. You take slashing damage equal to the amount of damage dealt this way.
71-80	The blade has started to attract followers, devout on fulfilling the purpose of the blade. If you are undertaking a quest that involves pursuing, hunting, or fighting creatures of the given type, the DM may allow 2 Cultist Hierophant's to accompany you on your quest. They listen to your commands (no action required) as long as you wield the Apocalypse Blade.
81-85	The Apocalypse Blade is able to unleash the souls stored within it. You may use the blade to cast Spirit Shroud, without requiring concentration. Once used, this ability cannot be used until the next dawn.
86-90	While attuned to the Apocalypse Blade, your Constitution Score and your Constitution Score Maximum increase by 2.
91-95	Attacks made by the Apocalypse Blade against creatures of the chosen type have advantage.
96-99	As an action, you may raise the Apocalypse Blade to the sky, and beseech the aid of whatever higher power created this blade. Immediately cast the Wish spell. Afterwards, the blade loses this property.
100	The blade determines itself to be complete - and unattunes itself from you. It teleports back to it's creator. If you are a celestial, you immediately become a Transformation Level 4 Seraph. If you were a Fiend, you become a Transformation Level 4 Fiend. If you are a Aberration, you become a Transformation Level 4 Aberrant Horror.

 

Cursed: While attuned to the Apocalypse Blade, you cannot willingly unattune to it. Breaking this attunement requires the use of the Wish spell, which you cannot do yourself. If you damage a creature of the chosen type with a weapon that is not the Apocalypse Blade, you take psychic damage equal to the damage that you dealt with that other weapon, which cannot be reduced in any way. Additionally, while attuned to this weapon, it twists your alignment- you seek and look for any reason that would fit within your given alignment and morality to kill creatures of the chosen type. 

Proficiency with a Greatsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: by a character who is a Celestial, Fiend, or Aberration , Heavy, Two-Handed, Graze