Spellcasting. Lothar is a 10th-level spellcaster. His spellcasting ability is Charisma (spell save DC 17, +9 to hit with spell attacks). Lothar has the following spells prepared:

• Cantrips (at will): acid splash, mage hand, prestidigitation, minor illusion
• 1st level (4 slots): charm person, disguise self, shield, magic missile
• 2nd level (3 slots): suggestion, misty step, acid arrow
• 3rd level (3 slots): counterspell, fear, fly
• 4th level (3 slots): greater invisibility, polymorph, dominate person
• 5th level (2 slots): cloudkill, major image

Dragon's Staff. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: (1d6 + 4 bludgeoning + 3d6 acid

Acid Breath (Recharge 5–6). Lothar exhales acid in a 30-foot line that is 5 feet wide. Each creature in that line must make a DC 15 Dexterity saving throw, taking (5d8 acid damage on a failed save, or half as much damage on a successful one.

Hidden Dragon. If dropped to 0 hit points, Lothar can use his reaction to polymorph back into his true form, that of an ancient black dragon. In the transformation, he gains the health of an ancient black dragon, but minus the HP of this form.

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

Spellcasting (Costs 1 Action). Lothar casts a spell from his list of prepared spells, expending a spell slot as normal. 

Acidic Afterimage (Costs 2 Actions). Lothar instantly teleports up to 30 feet to an unoccupied space he can see. An acidic residue remains at the place he vanished from, and each creature within 5 feet of that space must succeed on a DC 15 Dexterity saving throw or take (2d6 acid damage.