Dark Shard Amulet

Weight/Price: 0 lb, 500 gp
Requires attunement by a warlock
Spellcasting focus for your warlock spells.
Try to cast a cantrip that you don't know.
Must be on the Warlock spell list, and you
must make a DC 10 Arcana check.
Success: you cast the spell.
One use per long rest.