Nightmare Sans

Special Trait Name. Enter the description for your special trait.

Spellcasting. The [monster name] is a 20-level spellcaster. Its spellcasting ability is [constitution] (spell save DC 18, +4 to hit with spell attacks). The [Nightmare Sans] has following [warlock], [wizard], and [sorcerer] spells prepared:
1st level (20 slots): [Absorb Elements], [Expeditious retreat], [Command] 

2st level (18 slots): [Alter Self], [Darkness]

3rd level (16 slots): [Fear], [Major Image], [Vampiric touch], [Blink]

4th level (15 slots): [Dominate Beast], [Black Tentacles]

5th level (15 slots): [Dominate person]

7th level (12 slots): [Teleport], [Finger of Death]

5th level (10 slots): [Dominate Monster]

Action Name.tentacle restraint:uses one of his four tentacles to restrain a target. The target must succeed in a DC 18 strength save to escape or have somebody else use their action to use a strength save on their behalf If they fail the save then they are stuck like that until they can succeed or until the user is defeated.

Action Melee Attack. multi-tentacle stab: +5 to hit, reach 5 ft., 1 target. Hit: 4 (4d20+32+CON modifier+CON modifier+CON modifier+CON modifier) [piercing] damage. 

Action Ranged Attack. tentacle stab: +10 to hit, reach 60 ft., 1 target. Hit: 1 (1d20+32+CON modifier- targets DEX modifier) [piercing] damage

tentacle slam: +3 to hit, reach Targets everything within a 15 by 40 path. Hit: 1 (1d20+10+CON modifier) [bludgeoning] damage

tentacle wip: +4 to hit, reach Targets everything within a 40 by 40 path. Hit: 1 (1d20+8+CON modifier) [bludgeoning] damage

Reaction Name. block:As a reaction He moves his tentacles in front of him to block an attack reducing the damage of the attack by 3/4

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

summon killer (Costs 1 Actions).  summon killer:Instantly teleport monster [Killer Sans] in front of him (cannot be used if he is already dead or already there)

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

summon the squad (Costs 4 Actions). Instantly teleport monsters [Killer Sans], [Dust Sans], [horror Sans], and [Insanity Sans] in front of him (Anybody who is already dead or already there will not be teleported)