Disintegration. If Primus dies, its body disintegrates into dust, leaving behind its weapons and anything else it was carrying.

Shapechanger. Primus can use its action to polymorph into a form that resembles a Medium humanoid, or back into its true form. Aside from its size, his statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed.

Legendary Resistance (3/Day). If Primus fails a saving throw, he can choose to succeed instead.

The One and the Prime. Attack rolls against Primus of 3 and lower count as critical failures.

Innate Spellcasting. Primus's spellcasting ability is wisdom (spell save DC 21, +9 to hit with spell attacks). Primus can innately cast the following spells, requiring no components.                                                                                                                                      At Will: forecage, prismatic spray, regenerate, finger of death                                                 2/day each: gate, mass heal, prismatic wall, feeblemind                                                       1/day each: demiplane, power word kill, wish

Multiattack. Primus makes 1 attack with is right arm and 1 attack with his left arm.

Right Arm. Melee Weapon Attack: +14 to hit, reach 15 ft., 1 target. Hit: 100 (10d20) necrotic damage.

Left Arm. Ranged Weapon Attack: +14 to hit, range 100/150 ft., 3 targets. Hit: 70 (7d20) radiant damage. Primus summons 4 Secundi to assist him. He can only do this once until the secondi disperse.

Summon Secundi. Primus summons 4 Secundi to assist him. He can only do this once until the secondi disperse.

Primus can take 5 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. Primus regains spent legendary actions at the start of its turn.

Shadow. Primus attacks with its right arm.

Light. Primus attacks one creature with his left arm.

Imprison (Costs 2 Actions). Primus casts Forecage.