Charon

The Ferryman. If Charon kills a creature, the creature must pay Charon 1 Dead Man's Coin or become a zombie servant to Charon.

Spellcasting. Charon is a 1,000th-level spellcaster. Its spellcasting ability is Dexterity (spell save DC 100, +999 to hit with spell attacks). Charon can cast any Necromancy spell at will at any level along with eldrich blast at any level.

The Ferryman's Oar. Melee Weapon Attack: +32 to hit, reach 120 ft., 5 targets. Hit: 539 (120d8) Necrotic damage. 

Unholy Screaming. RangedWeapon Attack: +45 to hit, range 1000/9999 ft., Unlimited targets. Hit: 650 (60d20) Necrotic damage.

Carry onward. Once each time another creature other than Charon attempts to target Charon for an attack of any kind, Charon can reflect the attack back at the creature with twice the effect.

Each turn Charon can take 2 Legendary actions (Charon cannot take a Legendary action on the same turn it takes a Mythic action)

Cast (Costs 1 Action). Charon casts a spell of its choice.

Charon can take 3 Mythic actions each turn (Charon cannot take a Mythic action on the same turn it takes a Legendary action)

All-out assault (Costs 3 Actions). Charon attacks with The Ferryman's Oar 15 times.