In the traits of the Doppelganger (https://www.dndbeyond.com/monsters/doppelganger), two traits are mistakenly smushed together into the same paragraph:

Ambusher. The doppelganger has advantage on attack rolls against any creature it has surprised. Surprise Attack. If the doppelganger surprises a creature and hits it with an attack during the first round of combat, the target takes an extra 10 (3d6) damage from the attack.

should be

Ambusher. The doppelganger has advantage on attack rolls against any creature it has surprised.

Surprise Attack. If the doppelganger surprises a creature and hits it with an attack during the first round of combat, the target takes an extra 10 (3d6) damage from the attack.

Good eye catching that.  I've updated that page to show correctly.  Thanks for the report!