Annihilation Well. Creatures that come within 50 ft of the Rogue Moon are effected by its dragging effect on the hulls of Spelljammers. If a Spelljammer comes within a mile of a Rogue Moon the occupant of its helm must make a DC 15 charisma check or have its will overwhelmed and be dragged towards the Rogue Moon.

Stony Carapace. The Rogue Moon is immune to spells not targeted at its maw, if a creature targeting the Rogue Moon cannot see its mouth when targeting it the spell misses.

Navigable surface. The Rogue Moon can be walked upon whilst inactive with ease, Whilst a creature is on its bulk the Rogue Moon has advantage on any tongue lash attacks and additionally can cast any spell an occupant knows.

Spike Burst.(Recharge 3) The Rogue Moon extrudes spikes from its shell, any creature within 30 feet or in contact with the Rogue moon takes 20 piercing damage

Tongue Lash. Melee Weapon Attack: +7 to hit, reach 20 ft., one target. Hit: 15 (2d10 + 5) Bludgeoning damage, additionally when hit by a Tongue lash a creature must make a DC 15 Strength saving throw or be knocked prone. This attack additionally deals siege damage.

A Rogue Moon gets 3 legendary actions a turn, taking them at initiative count 0 every turn. They are as follows:

Occlude Surface: (1 action) The Rogue Moon casts Wall of Stone

Destroyer Scales (2 actions) The Rogue Moon casts Erupting earth 

Orbital Drift (3 actions) (Recharge 5) The Rogue Moon casts Earthquake