PLUTO is a winner !!!!!
1) I have recently been demoted. The planet Pluto
2) I am someone you would not like to meet. Pluto (the Roman god of the underworld ruled over the land of the dead)
3) I once abducted a beautiful young lady who later became my wife. Pluto (as Hades in the Greek legend) abducted Persephone
4) You would have to cross water to be with me. The river Styx separates the land of the living from the land of the dead
5) My name is actually an alias. The alias of 'Hades'
6) Some people think that I am a dog; I am not, but I have a dreadful watchdog protecting my property. The Disney canine character Pluto. The three headed dog Cerberus guarded the entry to the land of the dead.
Your turn!!!