Your strength increases by 1, and your dexterity increases by 2.

You can breath both air and water. You also have a swim speed of 30 feet.

You can walk as silent as a crab, you have proficiency in Stealth

You have Blindsight for up to 30ft.

Your claws are a nasty natural weapon. You have a claw attack that does 1d6 bludgeoning plus your strength modifier. You can also use them to crush/cut certain items (rope, paper, clothing, wood, small rocks) after succeeding a STR DC Check, and pick up certain items (all within reason of course), though you can not use the item properly. You are crab.

You have a hard outer shell. As such, you have a natural armor of 15.

Your size is medium

You have a walking speed of 30 feet, like all Giant Crabs.

You can speak Common, plus one other language that might have been taught to you by the crazy wizard may have taught you.

You have the same age length of a Giant Crab

After making a successful hit with your claws, you may attempt to grapple as a Bonus action