Reliable independent sources support claims and establish notability per W:GNG. Reliable sources must be verifiable. Most print media from credible publishing houses have editors and are thus considered reliable in general. Expert self-published sources can be used to establish notability; be careful to follow BLP guidelines. For an overview of mainstream online sources considered reliable on Wikipedia see Wikipedia:Reliable sources and its derivative pages.
Horror or pop culture sites and publications deemed reliable (in rough alphabetical order)
Film Threat: The site started charging for reviews in 2011. Their current format does offer a free review option, but there is a heavy emphasis on purchasing a promotional package. Because of this, only reviews and articles dated to 2010 or earlier can be used to establish notability. Only people who have purchased a marketing package can receive a nomination for Film Threat's Award This! review. Because of that, and the overall lack of coverage in independent, secondary reliable sources, the award is also not usable for establishing notability.
HorrorNews.net, online here: HorrorNews.net began offering marketing/PR services in 2018. Anything published on the site before 2018 is usable for establishing notability; anything published after this date is not.
Horror Society, online here: Per this discussion, some journalists for the site use IMDb for information such as dates of birth and so on. The site is usable for reviews, but not for news stories that require fact checking.
iHorror, online here: iHorror began offering advertising by way of sponsored content in mid to late 2020. Wayback versions of their site as of June 2020 show an absence of an advertising page, so only reviews or coverage from this date or earlier should be considered reliable. The site does offer an award, however it does not appear to be notable enough to count towards notability due to the overall lack of coverage in independent, secondary reliable sources.
Shock Till You Drop was a horror website run through CraveOnline/Mandatory and Evolve Media. The site was merged into ComingSoon.net, which is currently engaged in pay-to-play. It is unknown if STYD engaged in this to any extent; Wayback showed no evidence for or against this. The consensus at the horror sourcing talk page was generally that the site is usable for its reviews and coverage on non-controversial topics while it was STYD. Anything published after it was turned into ComingSoon.net is not.
Questionable sources
Daily Dead, online here: The site does offer sponsored content, which they appear to have done since the site was launched. This content appears to be clearly marked. Anything marked as sponsored content cannot be used to establish notability. This will need to be run through WP:RS/N.
Unproven sources
Unproven sources are those which have not yet been examined by the project. They can not be used to establish notability.
CineGore, Hungarian site, can't make out exactly what is said but seems to be split off from a magazine
All Horror, does not have an "about page" but seems to have staff
Official websites
Many films, TV series, or other works have their own official websites, these can be reliable for claims about production and release dates, etc, but do not help establish notability.
Databases are collections of information from other places, databases can be reliable in cases like Box Office Mojo and The Numbers or they can be unreliable like IMDb. Databases in general are not good for establishing notability. Databases are often fit to be external links on articles.