Fragrite

Sand Camouflage (Sand Form Only). The fragrite has advantage on Dexterity (Stealth) checks made to hide in sandy terrain.

Sand Glide (Sand Form Only). The fragrite can burrow through sand without disturbing the material it moves through.

Shapechanger. As a bonus action, the fragrite can polymorph into a mass of sand or a glass humanoid. Its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. While in sand form, the fragrite has a burrow speed of 50 feet, it can move through a space as narrow as 1 inch wide without squeezing, and it is immune to the grappled condition. While in glass form, the fragrite has vulnerability to thunder damage.

Multiattack. The fragrite makes two strike attacks.

Strike. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 12 (2d8 + 3) bludgeoning damage. If the fragrite is in its glass form and has less than half of its total hp remaining, this attack instead deals 16 (3d8 + 3) slashing damage.

Spontaneous Explosion (Glass Form Only; Recharge 5-6). The fragrite explodes into shards of glass, reducing its hp by 5 (2d4). Each creature within 15 feet of it must make a DC 14 Dexterity saving throw, taking 27 (6d8) slashing damage on a failed save, or half as much damage on a successful one. The fragrite then polymorphs into its sand form.