Elemental Form. Aanoctanos can enter a creature's space and stop there. That creature takes 5d4 fire damage on each of its turns that Aanoctanos is in its space.

Spellcasting. Aanoctanos is an 18th-level spellcaster. Its spellcasting ability is Strength (spell save DC 17, +3 to hit with spell attacks). Aanoctanos has following wizard spells prepared:  
9th level (2 slots): meteor swarm, time stop 

Multiattack. Aanoctanos makes four attacks: two with its slam and two with its fire beam. It can substitute two of these for torrent or rock.

Slam. Melee Weapon Attack: +4 to hit, reach 5 ft., 1 target. Hit: 3d10 bludgeoning damage plus 1d12 fire damage. 

Rock. Ranged Weapon Attack: +4 to hit, range 50/150 ft., 1 target. Hit: 3d12 bludgeoning damage.

Torrent. Ranged Spell Attack: +5 to hit, range 10/300 ft., 1 target. Hit: 3d8 bludgeoning damage, and the target is pushed 50 ft. away.

Fire Beam. Ranged Spell Attack: +5 to hit, range 10/300 ft., 1 target. Hit: 3d8 fire damage.

Kinetic Release. When Aanoctanos is hit by an attack, it gains one charge. It can store a maximum of five charges. As a reaction when it takes damage, it can release any amount of charges. it does 2d12 fire damage for each charge released in this way.