Vampiric Mist

[OrlockDelesian]

I am running an old ad&d adventure, which calls for the pcs to face off with 3 vampiric mists.
Saddly whenever i Tweak older monsters I tend to either make them too easy or too hard.

My players are currently 9th lvl, and this encounter must be of the medium to hard variety.

Can anyone help me with updating the monster to 5th E?

[Aembrosia]

How many players?

[Aembrosia]

AC 15
Hit Points 90
Speed 0, fly 90 (hover)
Str0(-5) Dex 20(+5) Con14(+2) Int 6(-2) Wis 10 Cha 6(-2)
Damage Resistance Lightning, Thunder, Bludeoning Piercing and Slashing from Nonmagical Weapons.
Damage Immunity Poison
Condition Immunity Exhaustion, Grappled, Paralyzed, Petrified, Prone, Restrained, Unconscious
Sense Darkvision 60ft, Blood (autimatically pinpoints the location of blood within 60ft) Passive 10
Languages none?
CR ?? probably 5 but we need CR4

Air Form, its mist, it can occupy another creatures space cause its just vapor.

Blood Siphon and Blood Overdose hmm

You know what would make these annoying as all getout

Multiattack Vampiric Mist uses Blood Siphon Twice

Blood Siphon. Melee Weapon Attack: +6, Reach 0, one target. Hit: 12(2d6+5) //Damagetype?? A creature siphoned by Vampiric must must make a Con save DC 13 on a failed save their life force is drained by the vampiric Mist they take an additional 1d6//Damagetype??.

Blood overdose. Any additional damage dealt by Blood Siphon heals the Vampiric mist, it may take a bonus action disengage.

This is probably CR5, if you have 5 players, 3 of these would be a hard encounter. Scale the damage back a bit and it might be a 4. Three CR4's would be medium.

I dont know how many players you have so I cant fine tune it. And when I say fine tune it I mean pretend I have any idea what im talking about.

[OrlockDelesian]

Aembrosia I am officially naming an NpC after you in my campaign!

Thank you sir! You are a gentleman and a scholar. Go into my stable and take my finest stallion. He's yours, his name is Windjammer!