In-Game Resources
Find the pregenerated 5E characters for the one-shot.
Several printable versions of the letter from William Withers to give to your players.
Some options for the Graveyard Stage and Orchestra fight.
Here is a perfect map for it from Eightfold Paper on Patreon.
And an excellent free option from Angela Maps.
OSE textboxes for all of the monsters in the first issue.