Archfiend's Vessel, Legendary

Fiendish Resistance. The vessel has advantage on saving throws against being charmed, poisoned, or frightened.

Legendary Resistance (1/Day). If the vessel fails a saving throw, it can choose to succeed instead.

Eldritch Invocations. The vessel knows the following Eldritch Invocations:

• Agonizing Blast: Add CHA modifier to damage dealt by eldritch blast spell.
• Tomb of Levistus (1/Short or Long Rest): As a reaction when you take damage, you can entomb yourself in ice, which melts away at the end of your next turn. You gain 10 temporary hit points per warlock level, which take as much of the triggering damage as possible. You also gain vulnerability to fire damage, your speed drops to 0, and you are incapacitated. All of these effects end when the ice melts.

Shortsword. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) piercing damage and the target must make a DC 17 Constitution saving throw, taking 9 (2d8) poison or necrotic damage (vessel's choice) on a failure, or half as much on a success. Either the vessel or one of its allies then regains hit points equal to half the amount of poison or necrotic damage dealt.

Knife. Melee Weapon Attack: +6 to hit, reach 5 ft. or range 10/30 ft., one target. Hit: 3 piercing or slashing damage (vessel's choice).

Spellcasting. The vessel casts one of the following spells, using Charisma as the spellcasting ability (spell save DC 15, +7 to hit with spell attacks):

At will: eldritch blast, corruption, friends, cause fear, minor illusion, message, crown of madness, hellish rebuke

1/day each: enthrall, summon undead, banishment, counterspell, demon within, elemental bane, channel fiendish power

Harness Fiendish Power (2/Long Rest). The vessel channels the terrible power of its patron archfiend and regains one "1/day each" spell slot.

Summon Fiendform (1/Day). In response to being reduced to 0 hit points, the vessel uses a last ditch effort to automatically kill itself, causing its body to disintegrate into dark energy, leaving its equipment behind. Their is then a 80% chance that the vessel then summons a horrific apparition of its fiendish master, which has the stat block of any Fiend of CR 11 or lower. The summoned fiendish apparition remains for 10 minutes or until reduced to 0 hit points.

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

Strike. The vessel makes a melee attack.

Invoke Command. The vessel lets out a fiendish command to one Undead or Fiend that is under its control that is within 30 feet of it. If that creature can see and hear the vessel, it can use its reaction to make one melee attack with disadvantage or move up to half its speed.

Spell Blast (Costs 2 Actions). The vessel casts one of its "1/day each" damaging spells, with the save DC being increased by 1 if the spell requires a saving throw.