The Jeckyl and Hyde theory have merit, with things going for both that and the werewolf interpretation. I've always presumed the werewolf was being talked about in this song. The "feed my soul" part suggests werewolf, because werewolves feed and Jeckyl doesn't really feed. The "beneath an eerie moon" also suggests werewolf because the moon seems to be emphasized. However, "Of my alchemy" and "of my design" both suggest Jeckyl. Both could work.
The Jeckyl and Hyde theory have merit, with things going for both that and the werewolf interpretation. I've always presumed the werewolf was being talked about in this song. The "feed my soul" part suggests werewolf, because werewolves feed and Jeckyl doesn't really feed. The "beneath an eerie moon" also suggests werewolf because the moon seems to be emphasized. However, "Of my alchemy" and "of my design" both suggest Jeckyl. Both could work.