In this case, we have to be.  You can use your hands to get a lot of the shaping done into the leather, but that only works for the gross work.  The details have to be attended to with tools.

There are two basic tools we are using here.  The first is a bone awl.  This is actually used as a sort of reinforced thumb to push the leather into smaller cracks and features on the mask.
 
 
 
 

We are also using a horn hammer.

Making those was a real pain.  Basically they are a bull horn with a hole drilled through them and a hammer handle inserted.  Doesn't sound like much, but it took a lot more work to make them right then we first thought.

The tip of the horn also had to be sanded down to a rounder point so as not to split or cut the leather, but that was pretty straight forward.  The end result is this tool here.

Using the hammer dimples the leather against the surface underneath it, compressing the leather.

This seems to be to help it keep it's shape better.  Once that's done, the dimples can be smoothed out again using the bone awl.