Magic Resistance. The death knight has advantage on saving throws against spells and other magical effects.

Spectral Form. The Corrupted Monk can move through creatures and objects as if they were difficult terrain. If it ends its turn inside an object, it takes 10 force damage.

Phase Two — True Corruption. When the Corrupted Monk reaches zero hitpoints

• black centipedes erupt from beneath its robes and replace its head
• The arena darkens
• Chanting fills the air

The monk gains:

Corrupted Frenzy. The monk makes one additional Phantom Naginata attack during Multiattack.

Aura of Terror. Enemies starting their turn within 10 feet must succeed on a DC 15 Wisdom saving throw or become frightened until the start of their next turn.

Multiattack. The Corrupted Monk makes three attacks with its Phantom Naginata. (four at phase 2)

Phantom Naginata. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 15 (2d8 + 6) slashing damage plus 7 (2d6) necrotic damage.

Sweeping Perilous Attack. The monk spins its naginata in a massive sweep. Each creature within 15 feet must make a DC 16 Dexterity saving throw.

• Failure: 21 (6d6) slashing damage and knocked prone.
• Success: Half damage and not knocked prone.

Shadow Step. The monk teleports up to 20 feet to an unoccupied space it can see.

Acid Spit. The monk spits deathly acid upon its target, causing 3d6 acid damage on a failed DC 17 DEX save and none on a successful save.

Deflect. The monk adds +3 AC against one melee attack that would hit it. If the attack misses, the attacker takes 5 slashing damage.