Marshadow

This is the Mythical that gives Genesect a run for its money as my favorite Mythical Pokemon.  When I got my own Marshadow during the Marshadow event back in October, I wanted to know how this thing would play.  Turns out, it is a BEAST on the battlefield.  Being the only Fighting/Ghost type, it has a lot to bring, especially in terms of speed and physical attack, both being at 125.  With moves like Endeavor, Close Combat, Force Palm, Shadow Ball, Role Play and the Elemental Punches, Marshadow can tackle almost any opponent.  My favorite Marshadow move however has got to be its signature move, Spectral Thief.  Spectral Thief allows Marshadow to steal stat changes from an opponent, making itself stronger, while also doing damage.  It even comes with its own Z-Crystal, Marshadium Z, changing Spectral Thief into the devastating Soul Stealing Seven Star Strike. 
Now that's not all I like about Marshadow.  Its concept is also creative.  Marshadow is based on Shadow Boxing which is very fitting, seeing as according to its Pokedex entries, it hides in peoples shadows, mimicking their fighting styles.

Because of all this, Marshadow has not only become one of my favorite Ghost types but also my second favorite Fighting Type.