Corrupted_Oni V1

Monster traits. The Corrupted Oni possesses the following traits; Merciless, Hyper intelligent, Sanguine

Legendary Resistance (2/Day). If the Corrupted Oni fails a saving throw, it can choose to succeed instead.

Innate Invisibility. The Corrupted Oni is under the constant influence of greater invisibility until the Oni takes 20 points of fire damage in one turn. The Invisibility refreshes every dusk. 

Annihilation (1/day). The corrupted Oni's Volkin Spear hums to life, the Volkin Spear forces one creature within 30 feet to make a strength save (DC 10) or be pulled into the Spear leaving no trace. If invisible the creature has disadvantage on the save. If the blade is destroyed all bodies will be dropped on the ground in a heap, all dead but with the ability to be revived. 

Innate Spellcasting. The Corrupted Oni's innate spellcasting ability is Charisma (spell save DC 15). The Oni can innately cast the following spells, requiring no material components:

At will: darkness, invisibility

1/day each: charm person, cone of cold, gaseous form, sleep

Magic Weapons. The Corrupted Oni's weapon attacks are magical.

Regeneration. The Corrupted Oni regains 10 hit points at the start of its turn if it has at least 1 hit point. Unless it takes fire damage, if brought to 0 hit points by fire damage it is reduced to ash

Multiattack. The oni makes two attacks, either with its claws or its Gore Blade.

Claw (Oni Form Only). Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 8 (1d8 + 4) slashing damage.

Gore Blade. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 11 (2d6 + 4) slashing damage and Gain one bleed stack, or 7 (1d6 + 4) slashing damage and Gain one bleed stack in Small or Medium form.

Change Shape. The Corrupted Oni magically polymorphs into a Small or Medium humanoid, into a Large giant, or back into its true form. Other than its size, its statistics are the same in each form. The only equipment that is transformed is its Gore Blade, which shrinks so that it can be wielded in humanoid form. If the Corrupted Oni dies, it reverts to its true form, and its Gore Blade reverts to its normal size.

The Corrupted Oni's tactics for Volkin pull would be to pull the creatures into the Gore rot area to add more bleed stacks.

Volkin Pull. Two creatures of the Corrupted Oni's choice that is within 60 feet of the Corrupted Oni's must succeed on a DC 15 Strength saving throw or be pulled 30 feet closer to the Corrupted Oni. 

Bloodied State. When the Corrupted Oni is reduced to half its hp or less, It draws the Volkin spear from its chest in a last stitch effort to defeat its foes. This unlocks its bonus action abilities. In the bloodied state the Gore rot terrain will also trigger the creatures Bleed stack at the start of their turn.

Triggered action Horrid Reveal triggers when Innate Invisibility is broken. 

Horrid reveal. The Corrupted Oni exhales Terrifying Screech in a 30-foot cone. Each creature in that area must succeed on a DC 15 Wisdom saving throw. On a failed save, the creature is frightened from the Corrupted Oni.

The Corrupted Oni can take 2 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Corrupted Oni regains spent legendary actions at the start of its turn.

Mage Detection. The Corrupted Oni makes a Wisdom (Perception) check.

Gore Blade. The Corrupted Oni makes a Gore Blade attack.

Gore Rot (Costs 2 Actions)(Recharge 5–6). The Corrupted oni Slams its sword into the ground. Each creature within 10 feet wide and 30 feet long line of the Corrupted oni must succeed on a DC 15 Dexterity saving throw or take 11(2d6+4) Slashing damage and Gain one bleed stack.