Artifact lands are very popular in the format, as are many one and two-drop artifacts
If you have multiple copies of Unholy Annex on the battlefield, each one will trigger potentially burning your opponent for a ton of life
Also, theres a fuzzy but real benefit to presenting your opponent with lots of unknown questions with each face down creature you play-sure, that morph is probably a Rattleclaw Mystic or an Icefeather Aven but it could be a Sagu Mauler, and theres a small chance it could be something crazy like a Kheru Spellsnatcher

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Wrap Up Overlord of the Hauntwoods | Illustration by Tiffany Turrill There it is, the best cards from Duskmourn: House of Horror