I know I’m not normally the kind of guy who makes OCs based in existing properties, but the confirmed existence of Tartarus and thusly a Greek-model afterlife in MLP created an open space that I’d really like to see filled. Plus, I though this would compliment the whole “alicorn pantheon” thing the show seems to have going on.
 
Prince Felix is the ruler of Equestria’s underworld, a realm where the souls of ponies who have passed on spend their eternities in either paradise or suffering. Felix himself lives in a castle made almost entirely from solid gold and possesses riches beyond imagination. In spite of mortal ponies’ fear and aversion to him, he is largely passive to their affairs and rules over his subjects with stern, stoic hospitality. His beloved dog Cerberus, who guards the gates of Tartarus, is the one thing that warms his chilly heart.