You are a Monstrosity. You are also considered a shapechanger for any prerequisite or effect that requires you to be a shapechanger.

You are Medium.

Your walking speed is 30 feet.

You can use your action to polymorph into a Small or Medium humanoid you have seen, or back into your true form. Your statistics, other than your size, are the same in each form. Any equipment you are wearing or carrying isn't transformed. You revert to your true form if you die.

You have an advantage on attack rolls against any creature you have surprised.

If you surprise a creature and hit it with an attack during the first round of combat, the target takes an extra 3 (1d4) damage from the attack.

You magically read the surface thoughts of one creature within 60 feet of you. The effect can penetrate barriers, but 3 feet of wood or dirt, 2 feet of stone, 2 inches of metal, or a thin sheet of lead blocks it. While the target is in range, you can continue reading its thoughts, as long as your concentration isn't broken (as if concentrating on a spell). While reading the target's mind, you have an advantage on Wisdom (Insight) and Charisma (Deception, Intimidation, and Persuasion) checks against the target.