Magic Resistance.

The fungal servant has advantage on saving throws against spells and other magical effects.

Rejuvenation.

A destroyed fungal servant gains a new body in 24 hours if its heart is intact, regaining all its hit points and becoming active again. The new body appears within 5 feet of the fungal servant's heart.

Spellcasting.

The fungal servant is a 10th-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 17, +9 to hit with spell attacks). The fungal servant has the following cleric spells prepared:

Cantrips (at will): sacred flame, thaumaturgy
1st level (4 slots): command, guiding bolt, shield of faith
2nd level (3 slots): hold person, silence, spiritual weapon
3rd level (3 slots): animate dead, dispel magic
4th level (3 slots): divination, guardian of faith
5th level (2 slots): contagion, insect plague
6th level (1 slot): harm

Actions

Multiattack.

The fungal servant can use its Dreadful Glare and makes one attack with its rotting fist.

Rotting Fist.

Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 14 (3d6 + 4) bludgeoning damage plus 21 (6d6) necrotic damage. If the target is a creature, it must succeed on a DC 16 Constitution saving throw or be cursed with mummy rot. The cursed target can't regain hit points, and its hit point maximum decreases by 10 (3d6) for every 24 hours that elapse. If the curse reduces the target's hit point maximum to 0, the target dies, and its body turns to spores. The curse lasts until removed by the remove curse spell or other magic.

Dreadful Glare.

The fungal servant targets one creature it can see within 60 feet of it. If the target can see the fungal servant, it must succeed on a DC 16 Wisdom saving throw against this magic or become frightened until the end of the fungal servant's next turn. If the target fails the saving throw by 5 or more, it is also paralyzed for the same duration. A target that succeeds on the saving throw is immune to the Dreadful Glare of all fungal servants for the next 24 hours.

Legendary Actions

The fungal servant can take 3 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 fungal servant regains spent legendary actions at the start of its turn.

Attack. The fungal servant makes one attack with its rotting fist or uses its Dreadful Glare.
Blinding Spores. Blinding spores swirls magically around the fungal servant. Each creature within 5 feet of the fungal servant must succeed on a DC 16 Constitution saving throw or be blinded until the end of the creature's next turn.
Blasphemous Word (Costs 2 Actions). The fungal servant utters a blasphemous word. Each non-undead creature within 10 feet of the fungal servant that can hear the magical utterance must succeed on a DC 16 Constitution saving throw or be stunned until the end of the fungal servant's next turn.
Channel Negative Energy (Costs 2 Actions). The fungal servant magically unleashes negative energy. Creatures within 60 feet of the fungal servant, including ones behind barriers and around corners, can't regain hit points until the end of the fungal servant's next turn.
Whirlwind of Spores (Costs 2 Actions). The fungal servant magically transforms into a whirlwind of spores, moves up to 60 feet, and reverts to its normal form. While in whirlwind form, the fungal servant is immune to all damage, and it can't be grappled, petrified, knocked prone, restrained, or stunned. Equipment worn or carried by the fungal servant remain in its possession.

Fungal Servant