The Soul of Frostsilver

Earth Glide. The Soul of Frostsilver can burrow through nonmagical, unworked earth and stone. While doing so, the elemental doesn't disturb the material it moves through.

Siege Monster. The Soul of Frostsilver deals double damage to objects and structures.

Innate Spellcasting. The Soul of Frostsilver’s spellcasting ability is Strength (spell save DC 16). It can innately cast the following spells, requiring no material components:

At will: wall of stone

Multiattack. The elemental makes two Earthen Fist attacks.

Earthen Fist. Melee Weapon Attack: +8 to hit, reach 100 ft., one target. Hit: 14 (2d8 + 5) bludgeoning damage. If the attack hits, the target must succeed on a DC 15 Strength saving throw or be knocked prone. The Soul of Frostsilver can attack targets through the ground and wall of the Frostsilver Mine, with rocks and earth rising up to crush the target.

The Soul of Frostsilver can take 3 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 Soul of Frostsilver regains spent legendary actions at the start of its turn.

Earthen Fist. The Soul of Frostsilver makes one Earthen Fist attack.

Move Wall. The Soul of Frostsilver moves the wall of stone, reforming it as per the spell.

Wall of Stone (Costs 2 Actions). The Soul of Frostsilver casts wall of stone.