Night Caller

If you blow the whistle in darkness or under the
night sky, it allows you to cast the Animate Dead
spell. The target can be affected through up to
10 feet of soft earth or similar material, and if it
is, it takes 1 minute to claw its way to the surface
to serve you. Once thus used, the whistle can't be
used again until 7 days have passed.
You can blow the whistle to reassert control over
one or two creatures you animated with it once
every 24 hours.