Cursed, The Penitent Knight

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

Mage Slayer. The penitent knight has advantage on saving throws against spells cast by creatures within 10 feet of it. When a creature within 10 feet of the penitent knight casts a spell, the penitent knight can use its reaction to make one weapon attack against that creature. When the penitent knight damages a creature that is concentrating on a spell, that creature has disadvantage on the saving throw it makes to maintain its concentration.

Penitent Watcher. The penitent knight has advantage on Wisdom (perception) checks that rely on sight. If the penitent knight does not move on its turn, it has advantage on any Wisdom saving throws it makes until the start of its next turn.

Turning Immunity. The penitent knight is immune to effects and features that turn undead.

Undead Fortitude. If damage reduces the penitent knight to 0 hit points, it must make a constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the penitent knight is reduced to 1 hit point instead.

Multiattack. The penitent knight makes three weapon attacks; only one of which can be a Spark.

Greatsword. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 14 (3d6 + 4) slashing damage plus 7 (2d6) necrotic damage.

Spark. Ranged Weapon Attack: +8 to hit, range 10/30 ft., one target. Hit: 10 (3d6) fire damage and the target must succeed on a Dexterity saving throw (DC 15) or it catches fire; until someone takes an action to douse the fire, the target takes 7 (2d6) fire damage at the start of each of its turns.

Stomp. The penitent knight stomps its foot on the ground - creating a violent shockwave. Each creature other than the penitent knight within 15 feet must make a Strength saving throw (DC 15), taking 17 (5d6) bludgeoning damage on a failed save, and half (1/2) as much on a successful save. Creatures that fail the save by 5 or more are knocked prone.

Determined Advance. The penitent knight moves up to half (1/2) its speed, ignoring nonmagical difficult terrain; during this movement, any opportunity attacks made against the penitent knight have disadvantage.

Shield Wall.  When the penitent knight would be hit by a weapon attack or a spell that targets only the penitent knight; it may use its reaction to cause a wall of dirt, clay, stone, or bone (depending on the composition of the ground beneath its feet) to spring upward, interposed between the penitent knight and the source of the attack. This effect grants the penitent knight the benefit of the dodge action until the end of the attackers turn. The penitent knight must be aware of the attack in order to use this ability.

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

Attack. The penitent knight makes one weapon attack.

Perceive. The penitent knight makes a Wisdom (perception) check.

Dark Sanctuary. (Recharge 5-6, Costs 2 Actions). The penitent knight thrusts its sword into the ground, causing the earth to fracture in a 30 foot radius around it - turning the effected area into difficult terrain, this effect persists until the end of the penitent knight’s next turn. While holding its greatsword in the ground; the penitent knight cannot make greatsword attacks or spark attacks and its speed is reduced to 0. At the end of the penitent knight’s next turn; it pulls its greatsword from the ground, causing the area of difficult terrain around it to erupt with necrotic energy. Creatures in the area must make a Constitution saving throw (DC 15), taking 36 (8d8) necrotic damage on a failed save; and only half (1/2) as much damage on a successful save; and the penitent knight regains hit points equal to half (1/2) of the amount of necrotic damage dealt. Undead and Constructs do not take damage from this effect, although they are still subject to the difficult terrain created by it.