On casting bedevil, an annoying spirit was attached to the target, who needed to be on the same plane as the caster. This spirit annoyed the target. For example, the target saw some moving figment out of the corner of his or her eye, interrupting sleep, and so on. For arcane spellcasters, bedevil caused some real problems that went above simple annoyance. When an arcane spellcaster who became a target of this spell tried to cast a spell, the spirit disrupted this caster with a feeling of being haunted and being under observation. These disruptions could lead to failure of spellcasting. Bedevil had an extremely long duration that was measured in days.
The spirit's existence could be confirmed with a detect evil spell. They could be barred from annoying the target by casting protection from evil on the target. While it was impossible to rid the target of the spirit with a remove curse, it was possible with the dispel evil spell.
Bedevil required somatic, verbal, and material components. The material components were a statuette of a devil or imp and the target's blood; a drop was enough. The blood could be perfectly substituted with a personal object of the target.