The title of this article is conjectural. Though the topic is found within The Simpsons universe, a proper name is not available.
The Past Horrors couch gag is the fourth couch gag of Season 11.
The Simpsons are already on the couch, with Homer as a jack-in-the-box (from THOH II), Bart as a mutant fly (from THOH VIII), Marge as a witch (also from THOH VIII), and Maggie as an alien (from THOH IX). Lisa (as an ax murder victim) comments on the lackluster Halloween special hosted by Kang and Kodos ("What do aliens have to do with Halloween?"). Maggie yells in Kang's voice, "Silence!" and vaporizes Lisa with her ray-gun, before she puts her pacifier back on.