old lighter skull with spooky sound and flashing led

The black blob on the circuit board is a "COB" (chip-on-board) integrated circuit.
Modules like that are custom made for high sales volume, low cost items, eg. a similar construction is used for musical christmas cards etc.

There is no way of knowing what is in it.

You can get various LED flasher modules that could be adapted, or it's quite easy to build one with such as a 555 timer IC.
Examples:

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