Who or what is killed in the act of deicide?

easy to kill a god. deny they exist and then they don't exist

Deicide is very common in polytheistic mythology because gods are rarely considered all-powerful the way that monotheistic gods usually are. Usually they're killed by other gods, or by a mortal given some sort of divine power or weapon, often as part of godly infighting. Ancient mythology is pretty fascinating. Lots of tales of scheming, conflict and betrayal, like Game of Thrones on Mount Olympus.

Mythologies/ faiths/ religions/ cults/ beliefs,/ etc. (pick a term you prefer, they are all interchangeable). It is Groovy to learn the different lores of old & new.