A new Pokémon has been revealed for the upcoming Scarlet/Violet DLC, The Hidden Treasure of Area Zero
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Very little information has been revealed but it appears to be related to Terapagos (maybe a pre-evolution). The official site states:
This Pokémon is small in stature and not particularly strong, but when push comes to shove, it can crystallize the energy in its body to form a protective shield. Apparently, it can also assume a dormant state when it feels that its life is in danger by pulling its head, limbs, and tail into its shell and making itself look like a jewel.