From Pathfinder #195: Heavy is the Crown, which isn't enabled.

Tome of Dripping Shadows

ITEM 10

Price 1000 gp

Usage held in 1 hand

Bulk L

This book constantly drips evanescent tendrils of shadow that seethe and writhe. The tendrils have a will of their own, retreating from light sources and curling toward darkness. While you hold the tome, you gain darkvision; if you already have darkvision, you gain greater darkvision instead. Preparing spells from this tome strengthens your shadow magic and gives you a greater understanding of shadow spells you add to this tome. Any shadow spells you prepare from this tome that are at least 2 levels lower than the highest-rank spell you can cast are treated as 1 level higher for the purposes of counteracting them. When you add a shadow spell to this tome, you can prepare heightened versions of that spell up to the highest level of that spell that you are able to cast.

Activate envision

Frequency once per day

Trigger A target of a shadow spell you prepared from the grimoire critically fails a saving throw against the spell

Effect You recall a fragment of the shadow magic that suffuses your target and wrap it around yourself like a caul. The triggering creature's saving throw result is a failure, not a critical failure. For the next minute, you become Concealed to all creatures and you are Hidden from the triggering creature, regardless of what precise sense it has. If you use a hostile action against the triggering creature, you become only concealed to it (rather than hidden) at the end of the hostile action.

Pathfinder #195: Heavy is the CrownOGL