Death Burst.

When the Stonemelder dies, it turns to stone and explodes in a burst of rock shards, becoming a smoking pile of rubble. Each creature within 10 feet of the exploding Stonemelder must make a DC 14 Dexterity saving throw, taking 11 (2d10) bludgeoning damage on a failed save, or half as much damage on a successful one.

Spellcasting.

The Stonemelder is a 7th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 13, +5 to hit with spell attacks). It knows the following sorcerer spells:

Cantrips (at will): acid splash, blade ward, light, mending, mold earth
1st level (4 slots): expeditious retreat, false life, shield
2nd level (3 slots): Maximilian's earthen grasp, shatter
3rd level (3 slots): erupting earth, meld into stone
4th level (1 slot): stoneskin

Actions

Black Earth Rod.

Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) bludgeoning damage. The Stonemelder can also expend a spell slot to deal extra damage, dealing 2d8 bludgeoning damage for a 1st level slot, plus an additional 1d8 for each level of the slot above 1st.