Empowered attacks. The Bane's slam attacks are treated as magical and adamantine for the purpose of bypassing resistance and immunity to nonmagical weapons.
Innate Spellcasting. The Bane's innate spellcasting ability is Charisma (spell save 17, +9 to hit with spell attacks). It can innately cast the following spells, requiring no material components:
At will: meld into stone, move earth, wall of stone
Legendary resistance (1/Day). If the Bane fails a saving throw, it can choose to succeed instead.
Magic resistance. The Bane has advantage on saving throws against spells and other magical effects.
Multiattack. The Bane makes two slam attacks.
Slam. Melee weapon attack: +7 to hit, reach 15 ft., one target. Hit: 30 (4d10+8) bludgeoning damage.
Boulder. Range weapon attack: +3 to hit, range 500 ft. one target. Hit: 46 (7d10+8) bludgeoning damage.
Summon Elementals (1/Day). The bane summons up to three earth elementals and loses 30 hit points for each elemental he summons. Summoned elementals have maximum hit points, appear within 100 feet of the Bane, and disappear if the Bane is reduced to 0 hit points.
The Bane can take 1 legendary action. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Bane regains spent legendary actions at the start of its turn.
Illuminating Crystals. The bane's crystalline protrusions flare. Each creature within 30 feet of the Bane becomes outlined in orange light, shedding dim light in a 10-foot radius. Any attack roll against an affected creature has advantage if the attacker can see it, and the affected creature can't benefit from being invisible.