Preheat oven to 375°F (190°C) and position the rack in the middle.
Roll out the pie crust and gently press it into a 9-inch pie pan. Trim the edges if needed.
Use extra dough to cut out Halloween shapes like bats, pumpkins, or ghosts using cookie cutters or a small knife. Set aside.
In a mixing bowl, combine cherry pie filling, cornstarch, thawed cherries, lemon juice, and vanilla extract. Mix until evenly combined.
Pour the filling into the prepared crust and spread it evenly.
Beat the egg with 1 tablespoon of water to make an egg wash.
Brush the crust edge with egg wash. Add decorative cut-outs on top and brush them with egg wash as well.
Place the pie pan on a baking sheet (optional, to catch any drips) and bake for 45–55 minutes, or until the filling is bubbly and the crust is golden brown.
Let the pie cool on a wire rack before slicing to help the filling set.
Serve at room temperature or slightly warm.