From
http://dnd.wizards.com/articles/news/tomb-annihilation
+2 Con, +1 Wis (more likely)
or +2 Str, +1 Wis
Languages. Aquan (Maybe)
CLAWS. Your claws are natural weapons, which you can use to make unarmed strikes. If you hit with them, you deal slashing damage equal to 1d4 + your Strength modifier, instead of the bludgeoning damage normal for an unarmed strike.
HOLD BREATH. You can hold your breath for up to 1 hour at a time.
NATURAL ARMOR. Due to your shell and the shape of your body, you are ill-suited to wearing armor. Your shell provides ample protection, however; it gives you a base AC of 17 (your Dexterity modifier doesn’t affect this number). You gain no benefit from wearing armor, but if you are using a shield, you can apply the shield’s bonus as normal.
SHELL DEFENSE. You can withdraw into your shell as an action. Until you emerge, you gain a +4 bonus to AC, and you have advantage on Strength and Constitution saving throws. While in your shell, you are prone, your speed is 0 and can’t increase, you have disadvantage on Dexterity saving throws, you can’t take reactions, and the only action you can take is a bonus action to emerge from your shell.