Legendary Resistance (3/Day). Any time Irenicus would make a saving throw, he can choose to succeed instead of rolling.

Magic Resistance. Irenicus has advantage on saving throws against spells and other magical effects.

Live a Thousand Lives. Irenicus adds his proficiency bonus to all skill checks.

Aura of Harm. When an effect would restore hit points to a creature within 30 feet of Irenicus, the effect restores half as many hit points instead (rounded up).

Wizard Spellcasting. Irenicus is an 20th-level spellcaster. His spellcasting ability for arcane spells is Intelligence (spell save DC 21). Irenicus has the following spells prepared:

Cantrips (at will): blade ward, chill touch, mind sliver, mage hand

1st level (4 slots): gift of alacrity, magic missile, shield

2nd level (3 slots): blindness/deafness, suggestion*, trueform*

3rd level (3 slots): counterspell, major image*, sleet storm*

4th level (3 slots): charm monster, freedom of movement, gravity sinkhole

5th level (3 slots): steel wind strike, synaptic static, wall of force

6th level (2 slots): disintegrate, globe of invulnerability*, gravity fissure

7th level (2 slots): forcecage, prismatic spray

8th level (1 slot): dark star*, sunburst, 

9th level (1 slot): mordenkainen's disjunction

*Requires concentration

Solar Spellcasting. Irenicus's can spellcasting ability for divine spells is Charisma (spell save DC 24). He can innately cast the following spells, requiring no material components:

At will: alter self, invisibility* (self only)

3/day each: command, blade barrier*, dispel magic, resurrection

1/day each: earthquake*, power word pain

*Requires concentration

Multiattack. Irenicus makes an attack with his greatsword, then casts a spell using Wizard Spellcasting, using a spell slot as normal.

Greatsword. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 14 (2d6 + 7) slashing damage plus 11 (2d10) radiant damage and 11 (2d10) necrotic damage. On a critical hit, the sword emits a burst of light, and each creature other than Irenicus within 20 feet must make a DC 21 Dexterity saving throw, taking 28 (8d6) radiant damage on a failed save, or half as much damage on a successful one.

Slaying Longbow. Ranged Weapon Attack: +12 to hit, range 600 ft., one target. Hit: 28 (4d10 + 6) radiant damage. If the target is a creature that has 100 hit points or fewer, it must succeed on a DC 10 Constitution saving throw or die.

Reactive. Irenicus can take one reaction every turn in combat.

Riposte. Irenicus adds 6 to his AC against one melee attack. If the attack misses, Irenicus may immediately make one melee weapon attack against the creature that attacked him.

Shield. Irenicus casts shield, using a spell slot as normal.

Counterspell. Irenicus casts counterspell, using a spell slot as normal.

Irenicus can take 3 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. Irenicus regains spent legendary actions at the start of its turn.

Teleport. Irenicus magically teleports, along with any equipment he is wearing or carrying, up to 120 feet to an unoccupied space.

Attack. Irenicus makes an attack with his greatsword or slaying longbow.

Bleed the Soul. Irenicus chooses a creature he has hit with his greatsword since the beginning of his last turn. The creature must make a DC21 Constitution saving throw. On a failure, the target starts with 1 death saving throw failure the next time they are reduced to 0 hit points. This effect lasts until the target finishes a long rest.

Celestial Spell (Costs 2 Actions). Irenicus casts a spell using Solar Spellcasting, expending a spell as normal.