Fey Ancestry. The drider has advantage on saving throws against being charmed, and magic can't put the drider to sleep.

Spider Climb. The drider can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Sunlight Sensitivity. While in sunlight, the drider has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Web Walker. The drider ignores movement restrictions caused by webbing.

Spellcasting. Zasih is an Apprentice spellcaster (or granted spells by a patron of the DM's choice). Her spellcasting ability is Charisma (though spells are limited) (spell save DC 20, +8 to hit with spell attacks). Zasih has the following spells prepared:

(at will): Mage Hand, Shield, dancing lights

1/day each: darkness, faerie fire

1st level (4 slots): Detect Magic

2nd level (3 slots): Acid Arrow, Detect Thoughts, Invisibility, Mirror Image

3rd level (3 slots): Animate Dead, Counterspell

4th level (3 slots): Dimension Door

6th level (1 slot): Disintegrate

Multiattack. The drider makes three attacks, either with its longsword or its longbow. It can replace one of those attacks with a bite attack.

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: 2 (1d4) piercing damage plus 9 (2d8) poison damage.

Longsword. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) slashing damage, or 8 (1d10 + 3) slashing damage if used with two hands.

Longbow. Ranged Weapon Attack: +6 to hit, range 150/600 ft., one target. Hit: 7 (1d8 + 3) piercing damage plus 4 (1d8) poison damage.

Web. Ranged Weapon Attack: +9 to hit, range 60/120, one target. Hit: The target is Restrained by webbing. While restrained in this way, the target takes 3 (1d6) poison damage at the beginning of each of it's turns. As an action, the target can make a DC 18 Strength check, breaking free on a success. The webbing can also be attacked and destroyed (AC:12; HP:15; vulnerable to fire damage; immunity to bludgeoning, poison, and psychic damage).

Deadly Reach. In response to a visible enemy moving into its reach, Zasih makes one Longsword attack against that enemy.

Necromantic Healing. Zasih can regain hit points equal to the amount of necrotic/poison/acid damage that it is dealt 

Zasih can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. Zasih regains spent legendary actions at the start of its turn.

Cast Spell (Costs 1–3 Actions). Zasih uses a spell slot to cast a 1st-, 2nd-, or 3rd-level spell that it has prepared. Doing so costs 1 legendary action per level of the spell and does not burn a spell slot.

Cocoon. Zasih leaps up to 60 feet onto a target that is restrained by her web attack and attempts to wrap the target until it is completely cocooned. The target must make a DC 21 Strength saving throw, breaking away from Zasih on a success and becoming cocooned by Zasih on a failure. A cocooned creature is incapacitated. Allies may try to cut or burn away the cocoon (AC 12, HP 50; vulnerability to fire damage; immunity to bludgeoning, poison, and psychic damage). However, the cocooned target take half of any damage inflicted on the cocoon in this way.