Apparently when you leave a Poltergeist alone in the house, he may party with other unsavory undead fiends and watch sports. I imagine whenever KC is away on another of his wacky adventures the Poltergeist is drinking beer and probably holding fantasy baseball drafts other ghouls.
Jerry is a Lich but clearly not a very powerful one. A Lich is usually a magically infused undead being created out of the body of a sorcerer or mage who had undergone preparations to transform into an immortal undead being. Usually to carry out orders and serve demons or to acquire power and access to the afterlife. It’s a dirty messy business that most respectable people do not aspire to.
Worst of all Jerry is a Duke fan which is the only unforgivable part of his personality…