Arguably, the DW Druid's shapeshift the most controversial move in the main playbooks. I've seen lots of fixes for it; and i have my very own (which is casually the best!)
You can call upon the spirits to change your shape at will, into any species' whose essence you have studied or who lives in your land: you and your possessions meld into a perfect copy of the species’ form. You have any innate abilities and weaknesses of the form: claws, wings, gills, breathing water instead of air. You still use your normal stats but some moves may be harder to trigger—a housecat will find it hard to do battle with an ogre. The GM will also tell you one or more moves associated with your new form.
Whenever you're in this state, the moves "letting the beast act instead" and "losing yourself into the beast" are available to your GM.
Yes; this involves no dice rolls, nor even any specific mod. In certain occassions, a DEFY DANGER (+ WIS) can be called for to keeping a clear head amongst all the animal instincts.