Werecreatures are those shapeshifters that can only change into one alternate form. What they lack in flexibility and form options they make up for in the ability to specialize and be the very best shapeshifter of their type they can be.
Some of these shapeshifters are naturally born with the potential - a "minor talent" who's somewhat less minor than most - or have put in years of hard work learning how to do it, much like those who learn to take on a Wereform. Others are tied more directly with mythology; perhaps you've been infused with a drop from Ceridwen's cauldron, or you're a descendant of a trickster like Loki or Coyote.
Musts
Werecreatures must have a high concept that in some way indicates their supernatural ability.
Werecreatures must take the Physical Transformation condition.