Axiomatic Mind. The secundus can't be compelled to act in a manner contrary to its nature or its instructions. 

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

Innate Spellcasting. The secundus's innate spellcasting ability is intelligence (spell save DC 18) . It can innately cast the following spells, requiring no components:
At will: Forecage, Mordenkainen's Sword, Fire Storm                                                      2/day each: Antimagic Field, Sunburst, Teleport (self only)                                                   1/day: Imprisonment (chaining), Time Stop

Multiattack. The secondus makes two claw attacks.

Claw. Melee Weapon Attack: +12 to hit, reach 5 ft., # target. Hit: 30 (5d12) slashing damage and 50 (8d12+2) fire damage.

The secundus can take 4 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 secundus regains spent legendary actions at the start of its turn.

Dash. The secondus moves up to 60 feet.

Claw. The secondus makes a claw attack.

Blade (Costs 2 Actions). The secondus casts Mordenkainen's Sword