Book Wurm

Marked for Death. As long as a creature has at least one Poison Mark, it is Poisoned and must make a DC 13 Constitution saving throw each hour, taking 5(2d4) poison damage on a failed save, and half as much on a successful one. Also on a successful save, the target loses one Poison Mark. A Poison Mark can be removed by the protection from poison spell or similar magic. A creature with six or more Poison Marks falls Prone at the end of each of its turns. 

Paper Shaper. As a bonus action, the Book Wurm can fold or unfold its body. While the Book Wurm is folded and remains motionless, it is indistinguishable from a normal piece of paper. A successful DC 18 Intelligence(Investigation) check is required to discern that the Wurm is disguised.

Spell Storers. There is a 10% chance that a Book Wurm will have a spell written on its body, as they mimic pieces of paper. Roll a D10, treating each number as that level of spell, with a 1 being a Cantrip, and escalating from there. A creature that the Book Wurm considers friendly can cast that spell using the Wurm as an arcane or druidic focus, using their spell modifier to hit and spell save DC for the spell. 

Bite: Melee weapon attack, +6 to hit, reach 5ft, one target. Hit 1 piercing damage, and the target must make a DC 13 Constitution saving throw, taking 5(2d4) poison damage on a failed save, and half as much on a successful one. Additionally, on a failed save, the target gains a Poison Mark.