Dark Shard Amulet

You can use the amulet as a spellcasting focus for
your warlock spells. You can try to cast a cantrip
that you don't know. The cantrip must be on the Warlock spell list, and you must make a DC 10 Intelligence (Arcana) check. If the check
succeeds, you cast the spell. If the check fails, so
does the spell, and the action used to cast the
spell is wasted. In either case, you can't use this property again until you finish a long rest.