Deicide is the act of killing a god, or other deity. It is an act that is quite common in video games, as numerous titles in the fantasy genre often place the player at odds with an evil or corrupt god or goddess that must be stopped at any cost. God of War in particular is centered almost entirely around this concept, as Kratos is fueled by a lust for revenge against Ares for tricking him into killing his own family and people, and in the sequels takes this thirst even further by waging a one-man war against all of Olympus.
Shin Megami Tensei: Persona 4
In Persona 4, the investigation team eventually learns that all of the previous year's events in Inaba, from the serial murders to the kidnappings to the mysterious fog, were the result of an elaborate test conducted by Izanami, the ancient Japanese goddess of creation. At the game's end, the player's party must fight Izanami herself and defeat her so that the horrible events of the past year aren't repeated.
Thanks to the power of the dictionary in Super Scribblenauts, it's not only possible to summon a god, but also to kill him, should the player also summon the right creature or tools for the job.
Eternal Darkness: Sanity's Requiem
The story of Eternal Darkness, which stretches for millennia, is rooted in a three-way conflict between elder gods known as the ancients. These ancients, Xel'lotath, Ulyaoth, and Chattur'gha, pose a threat to all of humanity. The only way to ensure that they are all defeated is to play the game to completion three times, each representing a different alternate reality in which one of the ancients is killed by another at the end of the game.
Lightning Returns: Final Fantasy XIII
In Lightning Returns, Lightning is put forth on a mission by the almighty god Bhunivelze to save the souls of the living and gather Eradia to extend what little time the world has remaining before it's end. But in the end, when Bhunivelze's true intentions are unveiled, Lightning turns on him and with the aid of all of the world's souls, strikes him down.