Doppelganger

The monster makes two Slam attacks and uses Unsettling Visage if available.

(), reach..

The monster casts Detect Thoughts, requiring no spell components and using Charisma as the spellcasting ability.

You activate one of the effects below. Until the spell ends, you can activate either effect as a Magic action on your later turns. Sense Thoughts. You sense the presence of thoughts within 30 feet of yourself that belong to creatures that know languages or are telepathic. You don't read the thoughts, but you know that a thinking creature is present. The spell is blocked by 1 foot of stone, dirt, or wood; 1 inch of metal; or a thin sheet of lead. Read Thoughts. Target one creature you can see within 30 feet of yourself or one creature within 30 feet of yourself that you detected with the Sense Thoughts option. You learn what is most on the target's mind right now. If the target doesn't know any languages and isn't telepathic, you learn nothing. As a Magic action on your next turn, you can try to probe deeper into the target's mind. If you probe deeper, the target makes a Wisdom saving throw. On a failed save, you discern the target's reasoning, emotions, and something that looms large in its mind (such as a worry, love, or hate). On a successful save, the spell ends. Either way, the target knows that you are probing into its mind, and until you shift your attention away from the target's mind, the target can take an action on its turn to make an check against your spell save DC, ending the spell on a success.

Wisdom Save: DC 12. target: 15-foot radius, creature.

The monster shape-shifts into a, or it returns to its true form. Its game statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn't transformed.