Agramak, The Frostborn

Rimefrost. At the start of each of his turns Agramak has 20 Temp Hp, each time he takes damage the attacker suffer 5 cold damage whilst he has this temp hp.

Spellcasting. Agramak is a Spellcaster using Intelligence as its spellcasting modifier, and has a  +11 to hit, and a spell DC of 19 and cna cast the following spells:

1. 4 Chaos Bolt, Gift of Alacrity, Ice Knife, Magic Missle
2. 3 Misty Step, Rime's Binding Ice, Heat Metal (Cold)
3. 3 Haste, Fireball (Cold), Slow, Spirit Guardians 
4. 3 Banishment, Dimension door, Ice Storm
5. 2 Cone of Cold, Steel Wind Strike
6. 1 Wall of Ice

Multi-Attack. Agramak castes a spell or attacks with Frostmourne, and makes eitehr two snowball attacks or uses Cries of the Dead

Frostmourne. Melee Weapon Attack, +10 to hit, 1d10+4 Slashing, 2d6 Necrotic Damage, if this kills a target it steals their soul increasing the necrotic damage by 1d6 permanently.

Snowball Ranged Spell Attack, 120ft Range, +11 to hit, 2d10 Cold Damage.

Cries of the Dead: Each creature makes a DC 19 Wisdom Save, on a fail taking 3d10 Psychic Damage and becoming Frightened for 1 minute repeating the save at the end of each turn, if they pass they take half damage and are not frightened.

Incanter's Flow: If Agramak has successfully cast a spell this turn, he may cast another as a bonus action, he may still only concentrate on one spell at a time.

Quick Freeze: One Creature within 90ft makes a DC 19 Dexterity Save or becomes incapacitated frozen in ice, whilst in this state they are vulnerable to damage, doing 20 damage will break the ice, as will 1 point of fire damage, you are immune to fir damage.

Ice Nova. When a creature attempts to attack you you can use your reaction to make all creatures within 30ft make a DC 19 Dexterity Save, on a fail they are grappled, and you teleport 30ft away in a direction you choose. The ice lasts until the end of the creatures next turn, or they can attempt to break it the ice has 10 Hp, and an AC of 10.

Scream of Agony: When a creature you see within 90ft attempts to cast a spell, you can have them make a DC 19 Constitution Save, on a fail they take 4d8 Psychic Damage and the spell fails.

Agramak has 3 Legendary Action

Cast a Spell (Costs 1 Actions). Enter the description for your legendary action.

RISE! (costs 2 Action) Summoning 2 Frostguard at a point within 60ft you can see, Agramak cant have more than 3 out at once.

Cold Snap: (Costs 3 Actions) Each creature makes a DC 19 Constitutions Save on a fail taking 5d8 Cold Damage, this cannot drop a creature below 1 HP, and Incapacitates them til the end of their next turn, on a pass they take half damage and re not incapacitated.