What I was getting at with my comment about Denarians is that they do shapeshift and that some of their powers must obviously be unavailable in human form. For example: Hulking Size.
PS: Attacks against Might or Endurance might or might not be possible depending on how you read the rules. The only indication of a Might attack being possible is one example evocation. Endurance is mentioned as the defense skill against poisons and some environmental attacks, but not as something that players can aim attacks at. Personally, I choose to believe that the rules do not allow such attacks. If you want my reasons, I'll find a link to the thread where I argued this.