The Abyss Beckoners are a very rare pair of gloves that improve the damage resistance of summons at the risk of driving them mad.
Demons will bite their masters, slaves, comrades, and, on occasion, themselves. They bite on principle, and are functionally piranha with extra steps.
Properties
Gloves 
Rarity: Very Rare
Weight: 0.5 kg / 1 lb
Price: 450 gp
Special
The wearer of this item gains:
: The wearer's summoned creatures have resistance to all damage except 
Psychic damage. At the start of the summoned creatures turn, it must succeed a DC 13 
Wisdom saving throw or be driven Mad.
Where to find
Inside a locked chest in a cell, roughly X: 306 Y: -170 the Zhentarim Basement, The Risen Road.