This is the spellweaver lich I made for my Age of Worms campaign. It can cast up to 6 levels of spells per round (or 1 spell higher than 6th level). It can also burn legendary actions to cast levels of reaction spells. Thankfully the party just talked instead of doing its usual thing of picking a fight. Its opening would have been 2 fireballs. He can reliably boost his AC with shield and will win a counterspell duel, but it will cost lots of spell slots quickly. This one is obviously too powerful for your party, but you get the general idea.
Mak’ar
Medium undead, chaotic evil
Armor Class 15 (18 with mage armor)
Hit Points 97 (13d8 + 39)
Speed 30 ft.
STR DEX CON INT WIS CHA
8 (-1) 18 (+4) 16 (+3) 20 (+5) 14 (+2) 16 (+3)
Saving Throws Str +0, Dex +5, Con +10, Int +12, Wis +9, Cha +4
Skills Arcana +16, History +11, Insight +8, Perception +8
Damage Resistances cold, lightning, necrotic
Damage Immunities poison; bludgeoning, piercing, and
slashing from nonmagical weapons
Condition Immunities charmed, exhaustion, frightened,
paralyzed, poisoned
Senses truesight 120 ft., passive Perception 18
Languages Telepathy 1,000 miles
Challenge 17 (200 XP)
Special Equipment. Mak’ar has a cloak of protection.
Spell Weaving. Mak’ar can cast multiple spells during his turn
as long as the spell levels add up to 6 or fewer. He can only cast
one spell if its level is 6 or higher. Cantrips count as a 1st-level
spell for this purpose. Mak’ar can also concentrate on multiple
spells as long as the spell levels add up to 6 or fewer. He can
only concentrate on one spell if its level is 6 or higher. Mak’ar
can choose one or more spells to stop concentrating on if a new
concentration spell is cast that would put him over his limit.
When Mak’ar must make Concentration saving throws, he
makes a Concentration saving throw with advantage for each
spell that he is maintaining concentration.
Legendary Resistance (3/Day). If Mak’ar fails a saving throw,
he can choose to succeed instead.
Spellcasting. Mak’ar is a 16th-level spellcaster. Its spellcasting
ability is Intelligence (spell save DC 19, +11 to hit with spell
attacks). Mak’ar has the following wizard spells prepared:
Cantrips (at will):
1st level (4 slots): expeditious retreat, false life, mage armor,
magic missile, protection from evil and good, shield
2nd level (3 slots): blur, mirror image, ray of enfeeblement,
scorching ray
3rd level (3 slots): counterspell, dispel magic, fireball, slow,
vampiric touch
4th level (3 slots): confusion, fire shield
5th level (3 slots): cone of cold, contact other plane, hold
monster, wall of force
6th level (1 slot): chain lightning
7th level (1 slot): prismatic spray
8th level (1 slot): dominate monster, maze, power word stun
Turn Resistance. Mak’ar has advantage on saving throws
against any effect that turns undead.
Actions
Paralyzing Touch. Melee Spell Attack: +11 to hit, reach 5 ft.,
one creature. Hit: 10 (3d6) cold damage. The target must
succeed on a DC 18 Constitution saving throw or be paralyzed
for 1 minute. The target can repeat the saving throw at the end
of each of its turns, ending the effect on itself on a success.
Legendary Actions
The Mak’ar can take 6 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 (except
when taking a spell reaction). The Mak’ar regains spent
legendary actions at the start of its turn.
Spell Reaction (Cost Varies). The Mak’ar casts a spell with a
casting time of a reaction. The number of actions is equal to the
level of the spell. Mak’ar may take more than one Spell
Reaction per round.
Cantrip. The Mak’ar casts a cantrip.
Paralyzing Touch (Costs 2 Actions). The Mak’ar uses its
Paralyzing Touch.
Frightening Gaze (Costs 2 Actions). As per the lich (MM 202).
Disrupt Life (Costs 3 Actions). As per the lich (MM 202).
Mak’ar
Medium undead, chaotic evil
Armor Class 15 (18 with mage armor)
Hit Points 97 (13d8 + 39)
Speed 30 ft.
STR DEX CON INT WIS CHA
8 (-1) 18 (+4) 16 (+3) 20 (+5) 14 (+2) 16 (+3)
Saving Throws Str +0, Dex +5, Con +10, Int +12, Wis +9, Cha +4
Skills Arcana +16, History +11, Insight +8, Perception +8
Damage Resistances cold, lightning, necrotic
Damage Immunities poison; bludgeoning, piercing, and
slashing from nonmagical weapons
Condition Immunities charmed, exhaustion, frightened,
paralyzed, poisoned
Senses truesight 120 ft., passive Perception 18
Languages Telepathy 1,000 miles
Challenge 17 (200 XP)
Special Equipment. Mak’ar has a cloak of protection.
Spell Weaving. Mak’ar can cast multiple spells during his turn
as long as the spell levels add up to 6 or fewer. He can only cast
one spell if its level is 6 or higher. Cantrips count as a 1st-level
spell for this purpose. Mak’ar can also concentrate on multiple
spells as long as the spell levels add up to 6 or fewer. He can
only concentrate on one spell if its level is 6 or higher. Mak’ar
can choose one or more spells to stop concentrating on if a new
concentration spell is cast that would put him over his limit.
When Mak’ar must make Concentration saving throws, he
makes a Concentration saving throw with advantage for each
spell that he is maintaining concentration.
Legendary Resistance (3/Day). If Mak’ar fails a saving throw,
he can choose to succeed instead.
Spellcasting. Mak’ar is a 16th-level spellcaster. Its spellcasting
ability is Intelligence (spell save DC 19, +11 to hit with spell
attacks). Mak’ar has the following wizard spells prepared:
Cantrips (at will):
1st level (4 slots): expeditious retreat, false life, mage armor,
magic missile, protection from evil and good, shield
2nd level (3 slots): blur, mirror image, ray of enfeeblement,
scorching ray
3rd level (3 slots): counterspell, dispel magic, fireball, slow,
vampiric touch
4th level (3 slots): confusion, fire shield
5th level (3 slots): cone of cold, contact other plane, hold
monster, wall of force
6th level (1 slot): chain lightning
7th level (1 slot): prismatic spray
8th level (1 slot): dominate monster, maze, power word stun
Turn Resistance. Mak’ar has advantage on saving throws
against any effect that turns undead.
Actions
Paralyzing Touch. Melee Spell Attack: +11 to hit, reach 5 ft.,
one creature. Hit: 10 (3d6) cold damage. The target must
succeed on a DC 18 Constitution saving throw or be paralyzed
for 1 minute. The target can repeat the saving throw at the end
of each of its turns, ending the effect on itself on a success.
Legendary Actions
The Mak’ar can take 6 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 (except
when taking a spell reaction). The Mak’ar regains spent
legendary actions at the start of its turn.
Spell Reaction (Cost Varies). The Mak’ar casts a spell with a
casting time of a reaction. The number of actions is equal to the
level of the spell. Mak’ar may take more than one Spell
Reaction per round.
Cantrip. The Mak’ar casts a cantrip.
Paralyzing Touch (Costs 2 Actions). The Mak’ar uses its
Paralyzing Touch.
Frightening Gaze (Costs 2 Actions). As per the lich (MM 202).
Disrupt Life (Costs 3 Actions). As per the lich (MM 202).