Magic Items. Zaheil wears a cloak of protection and a Ring of Spell Storing that has a 5th level Counterspell stored in it. 

Spellcasting. Zaheil is a 12th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 16, +8 to hit with spell attacks). He has the following wizard spells prepared:

Cantrips (at will): lightning lure, dancing lights, mage hand, prestidigitation, ray of frost

1st level (4 slots): detect magic, tenser's floating disk, chromatic orb, shield, silent image

2nd level (3 slots): misty step, invisibility, darkvision

3rd level (3 slots): counterspell, lightning bolt, clairvoyance

4th level (3 slots): summon elemental, resilient sphere

5th level (2 slot): arcane hand, teleportation circle

6th level (1 slot): chain lightning

Dagger. Melee or Ranged Weapon Attack: +5 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 4 (1d4 + 2) piercing damage.