The druid has mastered their wild shape ability beyond that of normal druids and gain the following.

• The number of times a character can wildshape per rest is increased by 1
• The CR rating in which the character can take shape is increased by 1

In addition, the character can select unusual wildshape forms based on their Proficiency Bonus -1 (minimum 1).  This does not increase the number of uses per rest but only gives the player more options to choose from when selecting a wildshape.

• The creature type cannot be Humanoid, part humanoid, or have a humanoid shape (ex. no Centaurs, Driders, Satyrs, Harpies, Elves, Giants, Boggle...)
• The creature type cannot be Undead, Construct, or Elemental
• The new form cannot have lair or legendary actions and cannot cast spells
• The new shape must still abide by any class restrictions (see Druid wildshape table in PHB; plus CR increase from above)

The feat can only be taken once.