Darkshard Amulet

(requires attunement by a warlock)
•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.