Unknown Ancient Horror

• Grim Harvest. Once per turn when a living creature fails a saving throw against or is harmed by one of the Unknown Old Elders Necromancy spells of 1st level or higher, the necromancer regains hp equal to three times the spell’s level.
• Undead Thralls. When the necromancer casts animate dead, it can target one additional corpse or pile of bones, creating another zombie or skeleton, as appropriate. Undead created by the necromancer have an additional 9 hp and a +3 to their weapon damage rolls.
• Spellcasting. The Unkown Old Elder is a 10th-level spellcaster. Its primary spellcasting ability is Intelligence (spell save DC 15, +7 to hit with spell attacks). It has the following wizard spells prepared:
  • Cantrips (at will): chill touch, mage hand, poison spray, ray of frost
  • 1st level (4 slots): false life, mage armor, ray of sickness*
  • 2nd level (3 slots): blindness/deafness*, ray of enfeeblement*
  • 3rd level (3 slots): animate dead, dispel magic, fear, vampiric touch*
  • 4th level (3 slots): blight*, ice storm, stoneskin
  • 5th level (2 slots): cloudkill, cone of cold

     

Eldritch Animated Dead

10th-level necromancy

Casting Time: 30 sec
Range: 50 feet
Components: V, S, M (a drop of blood, a piece of flesh, and a pinch of bone dust)
Duration: Instantaneous

Cost: 3 Action Points

This spell creates an undead servant. Choose a pile of bones or a corpse of a Medium or Small humanoid within range. Your spell imbues the target with a foul mimicry of life, raising it as an undead creature. The target becomes a skeleton if you chose bones or a zombie if you chose a corpse (the DM has the creature’s game statistics).

On each of your turns, you can use a bonus action to mentally command any creature you made with this spell if the creature is within 60 feet of you (if you control multiple creatures, you can command any or all of them at the same time, issuing the same command to each one). You decide what action the creature will take and where it will move during its next turn, or you can issue a general command, such as to guard a particular chamber or corridor. If you issue no commands, the creature only defends itself against hostile creatures. Once given an order, the creature continues to follow it until its task is complete.

The creature is under your control for 24 hours, after which it stops obeying any command you’ve given it. To maintain the control of the creature for another 24 hours, you must cast this spell on the creature again before the current 24-hour period ends. This use of the spell reasserts your control over up to 18 creatures you have animated with this spell, rather than animating a new one.

Colossal Horror: After turn 7, colossal eldritch horror joins fight

 Frightful Presence. Each creature of the Unkown Great Elder's choice that is within 120 feet of the Unkown Great Elder and aware of it must succeed on a DC 17 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the Unkown Great Elder's Frightful Presence for the next 24 hours.

Aura of Apathy. Creatures within 1 mile of the monster’s lair experience a sensation of apathy and lack of will to go on. The sensation grows stronger the closer the creatures come to the monster’s lair and upon first seeing the monster, a creature must succeed on a DC (8 + Cha modifier + Proficiency Bonus) Wisdom saving throw or fall prone and become incapacitated when they first see the monster. This effect lasts until the end of their next turn as they are overcome with feelings of hopelessness.

Enter the description for how bonus actions work for your monster here.

Reaction Name. Enter the description for your action.

The Unknown Old Elder can take 5 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 Unknown Old Elder regains spent legendary actions at the start of its turn

Detect. Dagon makes a Wisdom (Perception) check.

Frightening Curse (Costs 3 Actions). The monster targets a creature within 30 feet of it that it can see and forces them to make a DC (8+Cha+Prof) Charisma saving throw. On a failed save, the target is cursed. While it is cursed, it has disadvantage on saving throws against being frightened and all allies of the monster have advantage on the first attack each round against the creature. This curse ends early if the monster is killed.

Can use legendary action points on mythic actions

Undead Sovereignty (Costs 2 Actions): Up to 5 Undead within 80 ft of Unknown Old Elder use their reaction to make a melee attack role. 

Negative Energy Burst (costs 3 action points):  Negative energy expands from the caster, doing 1d6+4 negative energy damage per caster level (Maximum damage 10d6+40 at CL:10) to all living enemies and friendly undead caught in the blast. A successful fortitude save reduces the damage by half. Undead are instead healed by the attack. Undead don't make the fortitude save for half healing. 

Pale masters or friendly creatures counted as Undead may use this spell to heal.