While not attuned to anybody and has two to all charges, the horns are a Small size piece of treasure worth 860 gp and will glow to produce dim light in a range of 5 feet when any crows, giant crows, blood hawks, vultures or other flesh/carrion eating birds are within 50 feet of them. If the amount of charges is depleted to one charge, this trait does not function.

While attuned, the horns have 4 charges. You can expend 1 charge to allow the darkened knowledge of the demon that once wore them into them you, increasing your Intelligence by 2 until 1 minute has passed.  You can also spend 2 charges to do multiple things. You can call forth the aid of up to three flesh/carrion-eating birds within 50 feet of you. The birds follow their own initiative count and are released from your service once they die or go farther than 150 feet away from you, you can gain advantage on all saving throws against magical effects for the next 4 minutes, or can cause sharp, pitch black fiendish claws to sprout from your fingernails, making your unarmed strike deal slashing damage instead of bludgeoning, make it that whenever you make an unarmed strike and hit, you gain hit points equal to half the damage dealt, and make it that your unarmed strike deals an extra 5 damage.  You can also spend all of the horn's charges to cause you to sprout large demonic wings (gaining a flying speed 50 feet), grow demonic claws (making your unarmed strike deal slashing damage and deal an extra 4 damage and make it that when you hit with an unarmed strike, you gain hit points equal to half the damage dealt), and gain Magic Resistance. Once 5 minutes have passed, the effect ends, and you must make a DC 15 Constitution saving throw, taking 7 (1d8+3) necrotic damage on a failed save, or half as much on a success. 

Once all of it's charges are spent, the horns become a non-magical piece of fancy material that are worth 860 gp.

Notes: Requires attunement from a warlock, druid, cleric, or paladin.