Augustine, Grave Vengeance

Evasion. When Augustine is not incapacitated and subjected to an effect that allows him to make a Dexterity saving throw to take only half damage, he instead takes no damage if he succeeds on the saving throw, and only half damage if it failed.

Reliable Talent. Whenever Augustine makes an ability check that includes his whole proficiency bonus, he can treat a d20 roll of 9 or lower as a 10.

Undead Fortitude. Augustine has Proficiency in Constitution Saving Throws.

Legendary Resistance (3/Day). If Augustine fails a saving throw, he may choose to succeed instead.

Multiattack. Augustine makes three attacks. One attack with Life Ender, and two attacks with Grave Marker.

Life Ender(Timepiercer). Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 15 (2d8 + 7) piercing damage plus 4 (1d8) necrotic damage. The target must succeed on a DC 17 Constitution saving throw or they are treated as if affected by the slow spell. This effect lasts for 1 minute, and the target can repeat this saving throw at the end of their turn to end this early.

Grave Marker(Frostbrand). Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 8 (1d6+5) piercing damage plus 3 (1d6) cold damage plus 3 (1d6) necrotic damage

Grave Pact (Recharge 6). Augustine summons 1d4 Large Husks (use the statblock of an Ogre Zombie). For each undead within 60 feet of Augustine, target creature that Augustine can see must make a DC 20 Strength saving throw as the life force of the living are syphoned to the returned monstrosities. On a failed save, The target takes 55 (10d10) necrotic damage and gets 2 Exhaution Points (Use OneD&D Exhaustion, cumulative penalty to d20 tests). The target takes half as much damage and gets no exhaustion points on a successful save.

Shadow Steps. Augustine magically teleports to an unoccupied space he can see up to 30 feet away. If there is a creature within 5 feet of where he teleported, and he hasn't attacked yet this turn, his next attack with Life Ender deals an extra 4d6 damage. 

Fade to Darkness (1/Day).  Immediately after you take damage, you can use your reaction to magically become invisible until the end of your next turn, or until you attack, deal damage or force a saving throw.

Augustine 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. Augustine regains spent legendary actions at the start of its turn.

Grave Marker. Augustine makes an attack with Grave Marker.

Dash. Augustine moves up to his movement speed. This movement doesn't incur attacks of opportunity.

Death's Embrace (Costs 3 Actions). If there is a creature within 30 feet of Augustine, and there are no other creatures within 5 feet of it, Augustine uses Shadow Steps, and makes one attack with Life Ender at that target. This attack is treated as a critical hit.