The Macabre Mob

[birdboye713]

If you are in a party with a Human Ranger named Buck Camel, look away now.

My party is about to fight a monster I created called a Macabre Mob. The party will be made of of 4 level 5 characters when they fight it.
It's meant to represent a node of unstable necrotic magic that animates bodies and gathers them into a horde.
If I could get some advice on balance, it would be appreciated.

Spoiler: Macabre Mob Statblock

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Macabre Mob
huge undead (swarm), neutral evil

Armor Class 13 (natural armor)
Hit Points 222
Speed 25 ft.(horde form only), 60 ft. flight(node form only)

Str
21(+5)
Dex
10(0)
Con
19(+4)
Int
10(0)
Wis
10(0)
Cha
8(-1)

Senses darkvision 60 ft. passive perception 10
Languages Abyssal
Challenge 8

Swarm The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a medium zombie. Any creature that starts its turn inside the same space as the Macabre Mob must make a dexterity saving throw (DC 15) or take 12 (4d6) bludgeoning damage, none on a success. The swarm can't regain hit points or gain temporary hit points unless another ability says it does.
Dispersing Swarm When the Macabre Mob is reduced to 100 hit points, its size is reduced to large. When the Macabre Mob reaches 30 hit points, it enters its node form, a tiny undead, it's strength becomes 6, and its dexterity becomes 19.

Actions
Multiattack (horde form only) The Macabre Mob makes two slam attacks.
Slam (horde form only) Melee Weapon Attack: +8 to hit , reach 5 ft., one target. Hit: 11 (2d6 + 5) bludgeoning damage.
Crawling Claw (horde form only) Ranged Weapon Attack: +8 to hit, ranged 20/60 ft., one target. Hit: 7 (1d4+5) bludgeoning or slashing damage (Mob’s choice)
Necrotic Beam (node form only) Ranged Spell Attack: +7 to hit, range 60 ft., one target. Hit: 14 (2d10+4) necrotic damage.
Awakening Aura (Recharge 5-6) Any dead humanoids or beasts within 300 ft. of the Macabre Mob that are not protected from becoming undead are turned into zombies.
Magnetic Aura (Recharge 5-6) Any undead with a Challenge Rating of 2 or lower within 120 ft. of the Macabre Mob must make a wisdom saving throw (DC 15) or become charmed for 1 minute and use all of their movement and dash to get as close to the Macabre Mob as possible. When it reaches the Macabre Mob, it becomes one with the Macabre Mob, and the Macabre Mob regains 20 hit points.

[JNAProductions]

Spoiler: Response

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That's... A lot of HP.

AFB at the moment, but this feels like it's almost certainly more than CR 8.

DCR
Base HP 222, AC 13. The auras feel unwieldy enough to probably not affect it.

OCR
(2*12)+(2*14)=24+28=52 DPR
At DC 15/+8 to-hit.

Okay, looking at the book...

Solid DCR 12 on stats alone.
And solid OCR 10.

That averages to 11, even WITHOUT accounting for special abilities.