Arachnophobia: Pretty straight-forward, all random encounters with spiders are prevented, and the game won’t let you in one spider-heavy location. Weirdly it DOES let you into another spider-heavy location (probably an oversight), but that place is optional and literally called “The Department of Spiders”, so if you still go there I think that’s on you.
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Arachnophilia: Every single combat has a spider added to the enemy side and a friendly spider added to your side.
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Arachnophonia: Replaces every single sound effect in combat with one of the ones that spiders make in the game. It is VERY unpleasant!