Ariel

Ariel is a Mimic, magically bound to the form of a book, by a paisley cage of copper and bronze with a locking clasp.  A powerful wizard once bound the mimic to be their repository of knowledge.  Once per day, a caster, or any creature within 5ft, can expend 1d4 hp per spell level to cast a known spell. If Ariel has been fed within 24hrs, the player has advantage on intelligence skill checks. 

Enthusiastic Bite:

If Ariel causes 15+ hp damage while feeding, the subject creature must succeed a 12 strength save or roll a d6 on the table below for appendages lost.
1- an eye, 2- a hand, 3- an ear, 4- a toe, 6- a finger