The Guard is a 10th Level Spellcaster. Its spellcasting modifier is Wisdom (Spell Save DC 15, +7 to hit with spell attacks). It has the following Artificer spells prepared:
Cantrips: Fire Bolt, Ray of Frost, Poison Spray
1st Level (4 Slots): Cure Wounds, Absorb Elements
2nd Level (3 Slots): Blur, Pyrotechnics
3rd Level (2 Slots): Haste
Unchanging Form. The Guard is immune to any spell or effect that would change its form.
Legendary Resistance (3/Day). If the Guard fails a saving throw it can choose to succeed instead.
Magical Resistance. The Guard has advantage on saving throws against spells and other magical effects.
Multiattack. The Guard makes two attacks, either a Crackling Backhand or Enflamed Stomp and a Slam attack. Crackling Backhand. Melee Weapon Attack: +16 to hit, reach 15ft., one target. Hit: (3d12 + 10) lightning damage. Enflamed Stomp. Melee Weapon Attack: +16 to hit, reach 10ft., one target. Hit: (3d10 + 10) fire damage. Slam. Melee Weapon Attack: +16 to hit, reach 15ft., one target. Hit: (3d8 + 10) bludgeoning damage. Prismatic Beam. The Guards internal crystal unleashes energy in a 60-foot line. Each creature in that area must make a DC 18 Dexterity saving throw, taking 40 (10d8) damage on a failed save, or half as much damage on a successful one. The damage is determined by rolling a d6:
The Guard 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. The Guard regains spent legendary actions at the start of their turn.
On initiative count 20 (losing initiative ties), the Guard can take a lair action to cause one of the following magical effects; the Guard can’t use the same effect two rounds in a row:
A large almost square room with rubble and large cylindrical pillars Around the room are 6 large clumps of crystals, which react when certain magic is cast on them. Some have positive effects some have negative effects: