Hypno. I adore Gengar, and would rather train one any day, but I think my encounter with one is more likely to be fatal than it necessarily would be with Hypno. Hypno is primarily interested in eatting your dreams. While that is creepy, Gengar hunts down people specifically to kill them, so they become ghosts, stuck with him in the afterlife. According to the Moon Dex entry, "It apparently wishes for a traveling companion. Since it was once human itself, it tries to create one by taking the lives of other humans."
Eat only boiling hot max soup with your face 3 times a day or eat anything you want, but have to stab your tongue with the sharp beak held item before each meal?