Beans the necrohampster

Spellcasting. The necrohampster is an 18th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 17, +9 to hit with spell attacks). The archmage can cast chromatic orb and mage armor at will and has the following wizard spells prepared:

Cantrips (at will): fire bolt, chill touch, mage hand, prestidigitation, shocking grasp

1st level (4 slots): cause fear, shield, mage armor, magic missile

2nd level (3 slots): melf's acid arrow, aganazzar's scorcher, nathair's mischief

3rd level (3 slots): summon lesser demons, summon undead, summon fey, animate dead

4th level (3 slots): summon greater demon, fabricate, stone shape*

5th level (3 slots): danse macabre, scrying, negative energy flood

6th level (1 slot): create undead, summon fiend

7th level (1 slot): symbol

8th level (1 slot): mighty fortress*

9th level (1 slot): imprisonment, wish

*The archmage casts these spells on itself before combat.

Multiattack. The necromancer makes three Arcane Burst attacks.

Shadow Bolt. Melee or Ranged Spell Attack: +7 to hit, reach 5 ft. or range 120 ft., one target. Hit: 20 (3d10 + 3) necrotic damage.

Dark Arts (1/Day). The necromancer magically summons any amount of demons or undead whose combined challenge rating does not exceed 9. The summoned creatures appear in unoccupied spaces within 60 feet of the necrohampster, whom they obey. They take their turns immediately after the necrohampster. Each lasts for 1 hour, until it or the necromancer dies, or until the necromancer dismisses it as a bonus action.