Axiomatic Mind.

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

Combat Ready.

The octon has advantage on initiative checks.

Disintegration.

If the octon dies, its body disintegrates into dust, leaving behind anything it was carrying.

Actions

Multiattack.

The octon makes three Tentacle attacks.

Tentacle.

Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 14 (3d6 + 4) bludgeoning damage plus 9 (2d8) lightning damage.

Spellcasting.

The octon casts one of the following spells, requiring no material components and using Intelligence as the spellcasting ability (spell save DC 15):

At will: detect magic, dispel magic, mending (as an action)
1/day each: plane shift (self only), protection from evil and good

Whirlwind of Tentacles (Recharge 5–6).

The octon rapidly extends and spins its ring of tentacles. Each creature within 20 feet of the octon must succeed on a DC 16 Strength saving throw or be pulled up to 10 feet in a straight line toward the octon. Then, the octon makes two Tentacle attacks against each creature within 10 feet of itself.

Octon Modron