Augmented Doppelgänger

Adaptable Form. The doppelgänger can alter its body as a bonus action, specializing toward 1 form of combat. It creates weapons & sometimes armor out of chitinous plates on its skin. Some of its actions have a form listed, like “Archer,” & the doppelgänger can only use these abilities while it's in the matching form. Abilities w/o a form listed can be used in any form. It can choose 1 of the following forms each time it uses this ability:

Archer Form – The doppelgänger has advantage on ranged weapon attacks & can use its reaction when a creature moves w/i 5 ft. of it to immediately move up to 10 ft. away from that creature w/o provoking opportunity attacks.

Knight Form – The doppelgänger gains a +3 bonus to its AC. Attack rolls against the doppelgänger's allies w/i 5 ft. of it've disadvantage.

Mage Form – The doppelganger can use its reaction to cast counterspell as a 3rd-level spell.

Shapechanger. The doppelgänger can use its action to polymorph into a Small or Medium humanoid it has seen or turn back into its true form. Its statistics, other than its size, are the same in each form. Any equipment it's wearing or carrying isn’t transformed. It reverts to its true form if it dies.

Multiattack. The doppelgänger makes 2 weapon attacks.

Halberd (Knight). Melee Weapon Attack: +7 to hit, reach 10 ft., 1 target. Hit: 15 (2d10 + 4) slashing damage & the target must succeed on a DC 15 Str saving throw or be knocked prone.

Lightning Arc (Mage). Ranged Spell Attack: +7 to hit, range 60 ft., 1 target. Hit: 27 (6d8) lightning damage & the target can’t take reactions until the start of its next turn. If this attack hits, the doppelgänger can use its bonus action to make an additional Lightning Arc attack against a different target w/i 15 ft. of the 1st target.

Longbow (Archer). Ranged Weapon Attack: +7 to hit, range 150/600 ft., 1 target. Hit: 13 (2d8 + 4) piercing damage & the target’s speed's reduced by 10 ft. until the end of its next turn.

Read Thoughts. The doppelgänger magically reads the surface thoughts of 1 creature w/i 60 ft. of it. The effect can penetrate barriers, but 3 ft. of wood or dirt, 2 ft. of stone, 2 in. of metal, or a thin sheet of lead blocks it. While the target's in range, the doppelgänger can continue reading its thoughts, as long as the doppelgänger's concentration isn’t broken (as if concentrating on a spell). While reading the target’s mind, the doppelganger has advantage on Wis (Insight) & Cha (Deception, Intimidation, & Persuasion) checks against the target.