Here are the stats taken from the write up in Verbosh booklet. They were not done in MM still, I put them that way, hope it is understandable.
Searvash
Climate/Terrain: Abyss
Frequency: unique?
Organization: solitary
Activity Cycle: any time
Diet: Intelligent creatures
Intelligence: High (14)
Treasure: I,Q
Alignment: Chaotic Evil
No. Appearing: 1
Armor Class: -2
Movement: 10, gaseous form 30
Hit Dice: 12 (110 hps)
THAC0: 9
No. of Attacks: 4
Damage/Attack: Tail? 1d6+poison, Bite 3d10, claws 2-12/2-12
Special Attacks: see below
Special Defenses: see below
Magic Resistance: 75%
Size: H (18' tall)
Morale: Champion (16)
XP Value: ?
Opening this door, a thick dark mist will come pouring out of the circular room, above that is the 9th level and top level of the tower. This mist causes all to save vs. fear or they will flee the tower by the shortest possible route presented to them. Note, this may mean out the door on 8th level (splat). This room has a central raised dias with a large chair of carved Ivory resting upon it. The demon of the mists, Searvash, was summoned out to the abyss by the original builder of the tower. Since the time of the first Wizard's death, Searvash has taken control of the tower. Searvash will be seated upon the ivory dias facing the party when they enter. As long as he is seated on the dias, all are affected as a symbol of, pain. While seated, Searvash has the ability to ESP anyone within the room.
Searvash has the following powers and attributes: AC: -2, HP: 110, fights as 12 HD. He appears as a semi-solid shape with a huge reptilian head, the entire body has a misted over type of appear¬ance that in the thick fog of the room makes it seem somewhat doubtful if there is really anything solid there at all. His normal move is 10" or he may choose to assume a gaseous form in which case his speed becomes 30". Searvash may do any of the following at will: Turn Rock to Mud (quicksand), Polymorph. Searvash may breath out a fog of poisonous gas once per three melee rounds, treat as a cloud kill with anyone not making saving throw going into a state of suspended animation until Searvash can eat the victim alive at his leisure. At any time, this demon may Dimension Door, Lightning or Gate in another demon. Gated demons will appear 75% of the time and the Gated demon may be Type I, 25%; Type II, 30%; Type III, 15%; Type IV, 10%; or Type V, 20% chance. Alone, Searvash gets 4 attacks per round. One does 1 - 6 points of damage and a save vs. poison is necessary. The teeth of this creature can inflict from 3 - 30 points of damage and the front claws can strike for 2 - 12 each. He can cause fear at will like a Fear Wand in addition to his mists that were mentioned earlier. He is also able to levitate and to emanate a Continual Dark spell at will.
He can cause disease at touch and in this case he gets a +2 chance to hit. A +1 or better weapon is required in order for any weapon to do him damage and as it is +1 weapons do only l/2 damage. His magic resistance is 75%, Holy Water will irritate him but will do no damage. However, a Purify Water spell cast upon him will do 1 six-sided die of damage for every 2 levels of the caster but against this, he gets a saving throw that halves damage if successful. If attacked psionically, he will strike back with a strength of 275 and he has all attack defense modes. In cases where he is not psionically attacked, he will usually not use psionics, preferring to use his other attack forms. If by some miracle, he is slain, before he can Dimension Door away or he has a chance to go gaseous and escape, Searvash is returned to the abyss.
Source: Judges Guild, Verbosh, pg 74, 1979
