Instead of "mettle, but just for will saves", why not give it Slippery Mind earlier? Or, rather, Partition Mind (from the Sanctified Mind).
In general, if you want to use some standard ability (ie, Mettle) I think you should just use Mettle.
I like Slippery Mind and Partition Mind though. Slippery First, Partition second.
Any reason you made the ghost step / ki uses swift and not immediate?